- 21 Mar, 2022 5 commits
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Jakub Sitnicki authored
In commit 9a69e2b3 ("bpf: Make remote_port field in struct bpf_sk_lookup 16-bit wide") the remote_port field has been split up and re-declared from u32 to be16. However, the accompanying changes to the context access converter have not been well thought through when it comes big-endian platforms. Today 2-byte wide loads from offsetof(struct bpf_sk_lookup, remote_port) are handled as narrow loads from a 4-byte wide field. This by itself is not enough to create a problem, but when we combine 1. 32-bit wide access to ->remote_port backed by a 16-wide wide load, with 2. inherent difference between litte- and big-endian in how narrow loads need have to be handled (see bpf_ctx_narrow_access_offset), we get inconsistent results for a 2-byte loads from &ctx->remote_port on LE and BE architectures. This in turn makes BPF C code for the common case of 2-byte load from ctx->remote_port not portable. To rectify it, inform the context access converter that remote_port is 2-byte wide field, and only 1-byte loads need to be treated as narrow loads. At the same time, we special-case the 4-byte load from &ctx->remote_port to continue handling it the same way as do today, in order to keep the existing BPF programs working. Fixes: 9a69e2b3 ("bpf: Make remote_port field in struct bpf_sk_lookup 16-bit wide") Signed-off-by:
Jakub Sitnicki <jakub@cloudflare.com> Signed-off-by:
Alexei Starovoitov <ast@kernel.org> Acked-by:
Martin KaFai Lau <kafai@fb.com> Link: https://lore.kernel.org/bpf/20220319183356.233666-2-jakub@cloudflare.com
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Alexei Starovoitov authored
Joanne Koong says: ==================== From: Joanne Koong <joannelkoong@gmail.com> Currently, local storage memory can only be allocated atomically (GFP_ATOMIC). This restriction is too strict for sleepable bpf programs. In this patchset, sleepable programs can allocate memory in local storage using GFP_KERNEL, while non-sleepable programs always default to GFP_ATOMIC. v3 <- v2: * Add extra case to local_storage.c selftest to test associating multiple elements with the local storage, which triggers a GFP_KERNEL allocation in local_storage_update(). * Cast gfp_t to __s32 in verifier to fix the sparse warnings v2 <- v1: * Allocate the memory before/after the raw_spin_lock_irqsave, depending on the gfp flags * Rename mem_flags to gfp_flags * Reword the comment "*mem_flags* is set by the bpf verifier" to "*gfp_flags* is a hidden argument provided by the verifier" * Add a sentence to the commit message about existing local storage selftests covering both the GFP_ATOMIC and GFP_KERNEL paths in bpf_local_storage_update. ==================== Signed-off-by: -
Joanne Koong authored
This patch adds a few calls to the existing local storage selftest to test that we can associate multiple elements with the local storage. The sleepable program's call to bpf_sk_storage_get with sk_storage_map2 will lead to an allocation of a new selem under the GFP_KERNEL flag. Signed-off-by:
Joanne Koong <joannelkoong@gmail.com> Signed-off-by:
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Joanne Koong authored
Currently, local storage memory can only be allocated atomically (GFP_ATOMIC). This restriction is too strict for sleepable bpf programs. In this patch, the verifier detects whether the program is sleepable, and passes the corresponding GFP_KERNEL or GFP_ATOMIC flag as a 5th argument to bpf_task/sk/inode_storage_get. This flag will propagate down to the local storage functions that allocate memory. Please note that bpf_task/sk/inode_storage_update_elem functions are invoked by userspace applications through syscalls. Preemption is disabled before bpf_task/sk/inode_storage_update_elem is called, which means they will always have to allocate memory atomically. Signed-off-by:
KP Singh <kpsingh@kernel.org> Acked-by:
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Andrii Nakryiko authored
If BPF object doesn't have an BTF info, don't attempt to search for BTF types describing BPF map key or value layout. Fixes: 262cfb74 ("libbpf: Init btf_{key,value}_type_id on internal map open") Signed-off-by:
Andrii Nakryiko <andrii@kernel.org> Signed-off-by:
Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20220320001911.3640917-1-andrii@kernel.org
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- 19 Mar, 2022 1 commit
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Kumar Kartikeya Dwivedi authored
Align it with helpers like bpf_find_btf_id, so all functions returning BTF in out parameter follow the same rule of raising reference consistently, regardless of module or vmlinux BTF. Adjust existing callers to handle the change accordinly. Signed-off-by:
Kumar Kartikeya Dwivedi <memxor@gmail.com> Signed-off-by:
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- 18 Mar, 2022 34 commits
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Kumar Kartikeya Dwivedi authored
In next few patches, we need a helper that searches all kernel BTFs (vmlinux and module BTFs), and finds the type denoted by 'name' and 'kind'. Turns out bpf_btf_find_by_name_kind already does the same thing, but it instead returns a BTF ID and optionally fd (if module BTF). This is used for relocating ksyms in BPF loader code (bpftool gen skel -L). We extract the core code out into a new helper bpf_find_btf_id, which returns the BTF ID in the return value, and BTF pointer in an out parameter. The reference for the returned BTF pointer is always raised, hence user must either transfer it (e.g. to a fd), or release it after use. Signed-off-by:
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Andrii Nakryiko authored
BPF_TRACE_KPROBE_MULTI is a new attach type name, add it to bpftool's table. This fixes a currently failing CI bpftool check. Signed-off-by:
Daniel Borkmann <daniel@iogearbox.net> Acked-by:
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Daniel Borkmann authored
Jakub Sitnicki says: ==================== I think we have reached a consensus [1] on how the test for the 4-byte load from bpf_sock->dst_port and bpf_sk_lookup->remote_port should look, so here goes v3. I will submit a separate set of patches for bpf_sk_lookup->remote_port tests. This series has been tested on x86_64 and s390 on top of recent bpf-next - ad13baf4 ("selftests/bpf: Test subprog jit when toggle bpf_jit_harden repeatedly"). [1] https://lore.kernel.org/bpf/87k0cwxkzs.fsf@cloudflare.com/ v2 -> v3: - Split what was previously patch 2 which was doing two things - Use BPF_TCP_* constants (Martin) - Treat the result of 4-byte load from dst_port as a 16-bit value (Martin) - Typo fixup and some rewording in patch 4 description v1 -> v2: - Limit read_sk_dst_port only to client traffic (patch 2) - Make read_sk_dst_port pass on litte- and big-endian (patch 3) v1: https://lore.kernel.org/bpf/20220225184130.483208-1-jakub@cloudflare.com/ v2: https://lore.kernel.org/bpf/20220227202757.519015-1-jakub@cloudflare.com/ ==================== Signed-off-by:
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Jakub Sitnicki authored
The check for 4-byte load from dst_port offset into bpf_sock is failing on big-endian architecture - s390. The bpf access converter rewrites the 4-byte load to a 2-byte load from sock_common at skc_dport offset, as shown below. * s390 / llvm-objdump -S --no-show-raw-insn 00000000000002a0 <sk_dst_port__load_word>: 84: r1 = *(u32 *)(r1 + 48) 85: w0 = 1 86: if w1 == 51966 goto +1 <LBB5_2> 87: w0 = 0 00000000000002c0 <LBB5_2>: 88: exit * s390 / bpftool prog dump xlated _Bool sk_dst_port__load_word(struct bpf_sock * sk): 35: (69) r1 = *(u16 *)(r1 +12) 36: (bc) w1 = w1 37: (b4) w0 = 1 38: (16) if w1 == 0xcafe goto pc+1 39: (b4) w0 = 0 40: (95) exit * x86_64 / llvm-objdump -S --no-show-raw-insn 00000000000002a0 <sk_dst_port__load_word>: 84: r1 = *(u32 *)(r1 + 48) 85: w0 = 1 86: if w1 == 65226 goto +1 <LBB5_2> 87: w0 = 0 00000000000002c0 <LBB5_2>: 88: exit * x86_64 / bpftool prog dump xlated _Bool sk_dst_port__load_word(struct bpf_sock * sk): 33: (69) r1 = *(u16 *)(r1 +12) 34: (b4) w0 = 1 35: (16) if w1 == 0xfeca goto pc+1 36: (b4) w0 = 0 37: (95) exit This leads to surprises if we treat the destination register contents as a 32-bit value, ignoring the fact that in reality it contains a 16-bit value. On little-endian the register contents reflect the bpf_sock struct definition, where the lower 16-bits contain the port number: struct bpf_sock { ... __be16 dst_port; /* offset 48 */ __u16 :16; ... }; However, on big-endian the register contents suggest that field the layout of bpf_sock struct is as so: struct bpf_sock { ... __u16 :16; /* offset 48 */ __be16 dst_port; ... }; Account for this quirky access conversion in the test case exercising the 4-byte load by treating the result as 16-bit wide. Signed-off-by: -
Jakub Sitnicki authored
Replace magic numbers in BPF code with constants from bpf.h, so that they don't require an explanation in the comments. Signed-off-by:
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Jakub Sitnicki authored
cgroup_skb/egress programs which sock_fields test installs process packets flying in both directions, from the client to the server, and in reverse direction. Recently added dst_port check relies on the fact that destination port (remote peer port) of the socket which sends the packet is known ahead of time. This holds true only for the client socket, which connects to the known server port. Filter out any traffic that is not egressing from the client socket in the BPF program that tests reading the dst_port. Fixes: 8f50f16f ("selftests/bpf: Extend verifier and bpf_sock tests for dst_port loads") Signed-off-by:
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Jakub Sitnicki authored
The helper macro that records an error in BPF programs that exercise sock fields access has been inadvertently broken by adaptation work that happened in commit b18c1f0a ("bpf: selftest: Adapt sock_fields test to use skel and global variables"). BPF_NOEXIST flag cannot be used to update BPF_MAP_TYPE_ARRAY. The operation always fails with -EEXIST, which in turn means the error never gets recorded, and the checks for errors always pass. Revert the change in update flags. Fixes: b18c1f0a ("bpf: selftest: Adapt sock_fields test to use skel and global variables") Signed-off-by:
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Andrii Nakryiko authored
Delyan Kratunov says: ==================== In the quest for ever more modularity, a new need has arisen - the ability to access data associated with a BPF library from a corresponding userspace library. The catch is that we don't want the userspace library to know about the structure of the final BPF object that the BPF library is linked into. In pursuit of this modularity, this patch series introduces *subskeletons.* Subskeletons are similar in use and design to skeletons with a couple of differences: 1. The generated storage types do not rely on contiguous storage for the library's variables because they may be interspersed randomly throughout the final BPF object's sections. 2. Subskeletons do not own objects and instead require a loaded bpf_object* to be passed at runtime in order to be initialized. By extension, symbols are resolved at runtime by parsing the final object's BTF. 3. Subskeletons allow access to all global variables, programs, and custom maps. They also expose the internal maps *of the final object*. This allows bpf_var_skeleton objects to contain a bpf_map** instead of a section name. Changes since v3: - Re-add key/value type lookup for legacy user maps (fixing btf test) - Minor cleanups (missed sanitize_identifier call, error messages, formatting) Changes since v2: - Reuse SEC_NAME strict mode flag - Init bpf_map->btf_value_type_id on open for internal maps *and* user BTF maps - Test custom section names (.data.foo) and overlapping kconfig externs between the final object and the library - Minor review comments in gen.c & libbpf.c Changes since v1: - Introduced new strict mode knob for single-routine-in-.text compatibility behavior, which disproportionately affects library objects. bpftool works in 1.0 mode so subskeleton generation doesn't have to worry about this now. - Made bpf_map_btf_value_type_id available earlier and used it wherever applicable. - Refactoring in bpftool gen.c per review comments. - Subskels now use typeof() for array and func proto globals to avoid the need for runtime split btf. - Expanded the subskeleton test to include arrays, custom maps, extern maps, weak symbols, and kconfigs. - selftests/bpf/Makefile now generates a subskel.h for every skel.h it would make. For reference, here is a shortened subskeleton header: #ifndef __TEST_SUBSKELETON_LIB_SUBSKEL_H__ #define __TEST_SUBSKELETON_LIB_SUBSKEL_H__ struct test_subskeleton_lib { struct bpf_object *obj; struct bpf_object_subskeleton *subskel; struct { struct bpf_map *map2; struct bpf_map *map1; struct bpf_map *data; struct bpf_map *rodata; struct bpf_map *bss; struct bpf_map *kconfig; } maps; struct { struct bpf_program *lib_perf_handler; } progs; struct test_subskeleton_lib__data { int *var6; int *var2; int *var5; } data; struct test_subskeleton_lib__rodata { int *var1; } rodata; struct test_subskeleton_lib__bss { struct { int var3_1; __s64 var3_2; } *var3; int *libout1; typeof(int[4]) *var4; typeof(int (*)()) *fn_ptr; } bss; struct test_subskeleton_lib__kconfig { _Bool *CONFIG_BPF_SYSCALL; } kconfig; static inline struct test_subskeleton_lib * test_subskeleton_lib__open(const struct bpf_object *src) { struct test_subskeleton_lib *obj; struct bpf_object_subskeleton *s; int err; ... s = (struct bpf_object_subskeleton *)calloc(1, sizeof(*s)); ... s->var_cnt = 9; ... s->vars[0].name = "var6"; s->vars[0].map = &obj->maps.data; s->vars[0].addr = (void**) &obj->data.var6; ... /* maps */ ... /* programs */ s->prog_cnt = 1; ... err = bpf_object__open_subskeleton(s); ... return obj; } #endif /* __TEST_SUBSKELETON_LIB_SUBSKEL_H__ */ ==================== Signed-off-by: -
Delyan Kratunov authored
This patch changes the selftests/bpf Makefile to also generate a subskel.h for every skel.h it would have normally generated. Separately, it also introduces a new subskeleton test which tests library objects, externs, weak symbols, kconfigs, and user maps. Signed-off-by:
Delyan Kratunov <delyank@fb.com> Signed-off-by:
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Delyan Kratunov authored
Subskeletons are headers which require an already loaded program to operate. For example, when a BPF library is linked into a larger BPF object file, the library userspace needs a way to access its own global variables without requiring knowledge about the larger program at build time. As a result, subskeletons require a loaded bpf_object to open(). Further, they find their own symbols in the larger program by walking BTF type data at run time. At this time, programs, maps, and globals are supported through non-owning pointers. Signed-off-by:
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Delyan Kratunov authored
In symmetry with bpf_object__open_skeleton(), bpf_object__open_subskeleton() performs the actual walking and linking of maps, progs, and globals described by bpf_*_skeleton objects. Signed-off-by:
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Delyan Kratunov authored
For internal and user maps, look up the key and value btf types on open() and not load(), so that `bpf_map_btf_value_type_id` is usable in `bpftool gen`. Signed-off-by:
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Delyan Kratunov authored
Currently, libbpf considers a single routine in .text to be a program. This is particularly confusing when it comes to library objects - a single routine meant to be used as an extern will instead be considered a bpf_program. This patch hides this compatibility behavior behind the pre-existing SEC_NAME strict mode flag. Signed-off-by:
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Alexei Starovoitov authored
Jiri Olsa says: ==================== hi, this patchset adds new link type BPF_TRACE_KPROBE_MULTI that attaches kprobe program through fprobe API [1] instroduced by Masami. The fprobe API allows to attach probe on multiple functions at once very fast, because it works on top of ftrace. On the other hand this limits the probe point to the function entry or return. With bpftrace support I see following attach speed: # perf stat --null -r 5 ./src/bpftrace -e 'kprobe:x* { } i:ms:1 { exit(); } ' Attaching 2 probes... Attaching 3342 functions ... 1.4960 +- 0.0285 seconds time elapsed ( +- 1.91% ) v3 changes: - based on latest fprobe post from Masami [2] - add acks - add extra comment to kprobe_multi_link_handler wrt entry ip setup [Masami] - keep swap_words_64 static and swap values directly in bpf_kprobe_multi_cookie_swap [Andrii] - rearrange locking/migrate setup in kprobe_multi_link_prog_run [Andrii] - move uapi fields [Andrii] - add bpf_program__attach_kprobe_multi_opts function [Andrii] - many small test changes [Andrii] - added tests for bpf_program__attach_kprobe_multi_opts - make kallsyms_lookup_name check for empty string [Andrii] v2 changes: - based on latest fprobe changes [1] - renaming the uapi interface to kprobe multi - adding support for sort_r to pass user pointer for swap functions and using that in cookie support to keep just single functions array - moving new link to kernel/trace/bpf_trace.c file - using single fprobe callback function for entry and exit - using kvzalloc, libbpf_ensure_mem functions - adding new k[ret]probe.multi sections instead of using current kprobe - used glob_match from test_progs.c, added '?' matching - move bpf_get_func_ip verifier inline change to seprate change - couple of other minor fixes Also available at: https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git bpf/kprobe_multi thanks, jirka [1] https://lore.kernel.org/bpf/164458044634.586276.3261555265565111183.stgit@devnote2/ [2] https://lore.kernel.org/bpf/164735281449.1084943.12438881786173547153.stgit@devnote2/ ==================== Signed-off-by: -
Jiri Olsa authored
Adding bpf_cookie test for programs attached by bpf_program__attach_kprobe_multi_opts API. Signed-off-by:
Jiri Olsa <jolsa@kernel.org> Signed-off-by:
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Jiri Olsa authored
Adding tests for bpf_program__attach_kprobe_multi_opts function, that test attach with pattern, symbols and addrs. Signed-off-by:
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Jiri Olsa authored
Adding bpf_cookie test for programs attached by kprobe_multi links. Signed-off-by:
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Jiri Olsa authored
Adding kprobe_multi attach test that uses new fprobe interface to attach kprobe program to multiple functions. The test is attaching programs to bpf_fentry_test* functions and uses single trampoline program bpf_prog_test_run to trigger bpf_fentry_test* functions. Signed-off-by:
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Jiri Olsa authored
Adding bpf_program__attach_kprobe_multi_opts function for attaching kprobe program to multiple functions. struct bpf_link * bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog, const char *pattern, const struct bpf_kprobe_multi_opts *opts); User can specify functions to attach with 'pattern' argument that allows wildcards (*?' supported) or provide symbols or addresses directly through opts argument. These 3 options are mutually exclusive. When using symbols or addresses, user can also provide cookie value for each symbol/address that can be retrieved later in bpf program with bpf_get_attach_cookie helper. struct bpf_kprobe_multi_opts { size_t sz; const char **syms; const unsigned long *addrs; const __u64 *cookies; size_t cnt; bool retprobe; size_t :0; }; Symbols, addresses and cookies are provided through opts object (syms/addrs/cookies) as array pointers with specified count (cnt). Each cookie value is paired with provided function address or symbol with the same array index. The program can be also attached as return probe if 'retprobe' is set. For quick usage with NULL opts argument, like: bpf_program__attach_kprobe_multi_opts(prog, "ksys_*", NULL) the 'prog' will be attached as kprobe to 'ksys_*' functions. Also adding new program sections for automatic attachment: kprobe.multi/<symbol_pattern> kretprobe.multi/<symbol_pattern> The symbol_pattern is used as 'pattern' argument in bpf_program__attach_kprobe_multi_opts function. Signed-off-by: -
Jiri Olsa authored
Adding new kprobe_multi struct to bpf_link_create_opts object to pass multiple kprobe data to link_create attr uapi. Signed-off-by:
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Jiri Olsa authored
Move the kallsyms parsing in internal libbpf_kallsyms_parse function, so it can be used from other places. It will be used in following changes. Signed-off-by:
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Jiri Olsa authored
Adding support to call bpf_get_attach_cookie helper from kprobe programs attached with kprobe multi link. The cookie is provided by array of u64 values, where each value is paired with provided function address or symbol with the same array index. When cookie array is provided it's sorted together with addresses (check bpf_kprobe_multi_cookie_swap). This way we can find cookie based on the address in bpf_get_attach_cookie helper. Suggested-by:
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Jiri Olsa authored
Adding support to inline it on x86, because it's single load instruction. Signed-off-by:
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Jiri Olsa authored
Adding support to call bpf_get_func_ip helper from kprobe programs attached by multi kprobe link. Signed-off-by:
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Alexei Starovoitov authored
Masami Hiramatsu says: ==================== Hi, Here is the 12th version of fprobe. This version fixes a possible gcc-11 issue which was reported as kretprobes on arm issue, and also I updated the fprobe document. The previous version (v11) is here[1]; [1] https://lore.kernel.org/all/164701432038.268462.3329725152949938527.stgit@devnote2/T/#u This series introduces the fprobe, the function entry/exit probe with multiple probe point support for x86, arm64 and powerpc64le. This also introduces the rethook for hooking function return as same as the kretprobe does. This abstraction will help us to generalize the fgraph tracer, because we can just switch to it from the rethook in fprobe, depending on the kernel configuration. The patch [1/12] is from Jiri's series[2]. [2] https://lore.kernel.org/all/20220104080943.113249-1-jolsa@kernel.org/T/#u And the patch [9/10] adds the FPROBE_FL_KPROBE_SHARED flag for the case if user wants to share the same code (or share a same resource) on the fprobe and the kprobes. I forcibly updated my kprobes/fprobe branch, you can pull this series from: https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git kprobes/fprobe Thank you, --- Jiri Olsa (1): ftrace: Add ftrace_set_filter_ips function ==================== Signed-off-by:
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Jiri Olsa authored
Adding new link type BPF_LINK_TYPE_KPROBE_MULTI that attaches kprobe program through fprobe API. The fprobe API allows to attach probe on multiple functions at once very fast, because it works on top of ftrace. On the other hand this limits the probe point to the function entry or return. The kprobe program gets the same pt_regs input ctx as when it's attached through the perf API. Adding new attach type BPF_TRACE_KPROBE_MULTI that allows attachment kprobe to multiple function with new link. User provides array of addresses or symbols with count to attach the kprobe program to. The new link_create uapi interface looks like: struct { __u32 flags; __u32 cnt; __aligned_u64 syms; __aligned_u64 addrs; } kprobe_multi; The flags field allows single BPF_TRACE_KPROBE_MULTI bit to create return multi kprobe. Signed-off-by:Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by:
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Jiri Olsa authored
When kallsyms_lookup_name is called with empty string, it will do futile search for it through all the symbols. Skipping the search for empty string. Signed-off-by:
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Jiri Olsa authored
Adding support to have priv pointer in swap callback function. Following the initial change on cmp callback functions [1] and adding SWAP_WRAPPER macro to identify sort call of sort_r. Signed-off-by:
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Masami Hiramatsu authored
Add a KUnit based selftest for fprobe interface. Signed-off-by:
Steven Rostedt (Google) <rostedt@goodmis.org> Tested-by:
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Masami Hiramatsu authored
Add a documentation of fprobe for the user who needs this interface. Signed-off-by:
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Masami Hiramatsu authored
Introduce FPROBE_FL_KPROBE_SHARED flag for sharing fprobe callback with kprobes safely from the viewpoint of recursion. Since the recursion safety of the fprobe (and ftrace) is a bit different from the kprobes, this may cause an issue if user wants to run the same code from the fprobe and the kprobes. The kprobes has per-cpu 'current_kprobe' variable which protects the kprobe handler from recursion in any case. On the other hand, the fprobe uses only ftrace_test_recursion_trylock(), which will allow interrupt context calls another (or same) fprobe during the fprobe user handler is running. This is not a matter in cases if the common callback shared among the kprobes and the fprobe has its own recursion detection, or it can handle the recursion in the different contexts (normal/interrupt/NMI.) But if it relies on the 'current_kprobe' recursion lock, it has to check kprobe_running() and use kprobe_busy_*() APIs. Fprobe has FPROBE_FL_KPROBE_SHARED flag to do this. If your common callback code will be shared with kprobes, please set FPROBE_FL_KPROBE_SHARED *before* registering the fprobe, like; fprobe.flags = FPROBE_FL_KPROBE_SHARED; register_fprobe(&fprobe, "func*", NULL); This will protect your common callback from the nested call. Signed-off-by:
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Masami Hiramatsu authored
Add a sample program for the fprobe. The sample_fprobe puts a fprobe on kernel_clone() by default. This dump stack and some called address info at the function entry and exit. The sample_fprobe.ko gets 2 parameters. - symbol: you can specify the comma separated symbols or wildcard symbol pattern (in this case you can not use comma) - stackdump: a bool value to enable or disable stack dump in the fprobe handler. Signed-off-by:
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Masami Hiramatsu authored
Add exit_handler to fprobe. fprobe + rethook allows us to hook the kernel function return. The rethook will be enabled only if the fprobe::exit_handler is set. Signed-off-by:
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Masami Hiramatsu authored
Add rethook arm implementation. Most of the code has been copied from kretprobes on arm. Since the arm's ftrace implementation is a bit special, this needs a special care using from fprobe. Signed-off-by:
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