- 05 Dec, 2018 40 commits
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Max Filippov authored
commit 03bc996a upstream. Coprocessor context offsets are used by the assembly code that moves coprocessor context between the individual fields of the thread_info::xtregs_cp structure and coprocessor registers. This fixes coprocessor context clobbering on flushing and reloading during normal user code execution and user process debugging in the presence of more than one coprocessor in the core configuration. Cc: stable@vger.kernel.org Signed-off-by:
Max Filippov <jcmvbkbc@gmail.com> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Max Filippov authored
commit 2958b666 upstream. coprocessor_flush_all may be called from a context of a thread that is different from the thread being flushed. In that case contents of the cpenable special register may not match ti->cpenable of the target thread, resulting in unhandled coprocessor exception in the kernel context. Set cpenable special register to the ti->cpenable of the target register for the duration of the flush and restore it afterwards. This fixes the following crash caused by coprocessor register inspection in native gdb: (gdb) p/x $w0 Illegal instruction in kernel: sig: 9 [#1] PREEMPT Call Trace: ___might_sleep+0x184/0x1a4 __might_sleep+0x41/0xac exit_signals+0x14/0x218 do_exit+0xc9/0x8b8 die+0x99/0xa0 do_illegal_instruction+0x18/0x6c common_exception+0x77/0x77 coprocessor_flush+0x16/0x3c arch_ptrace+0x46c/0x674 sys_ptrace+0x2ce/0x3b4 system_call+0x54/0x80 common_exception+0x77/0x77 note: gdb[100] exited with preempt_count 1 Killed Cc: stable@vger.kernel.org Signed-off-by:
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Wanpeng Li authored
commit e97f852f upstream. Reported by syzkaller: BUG: unable to handle kernel NULL pointer dereference at 00000000000001c8 PGD 80000003ec4da067 P4D 80000003ec4da067 PUD 3f7bfa067 PMD 0 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 7 PID: 5059 Comm: debug Tainted: G OE 4.19.0-rc5 #16 RIP: 0010:__lock_acquire+0x1a6/0x1990 Call Trace: lock_acquire+0xdb/0x210 _raw_spin_lock+0x38/0x70 kvm_ioapic_scan_entry+0x3e/0x110 [kvm] vcpu_enter_guest+0x167e/0x1910 [kvm] kvm_arch_vcpu_ioctl_run+0x35c/0x610 [kvm] kvm_vcpu_ioctl+0x3e9/0x6d0 [kvm] do_vfs_ioctl+0xa5/0x690 ksys_ioctl+0x6d/0x80 __x64_sys_ioctl+0x1a/0x20 do_syscall_64+0x83/0x6e0 entry_SYSCALL_64_after_hwframe+0x49/0xbe The reason is that the testcase writes hyperv synic HV_X64_MSR_SINT6 msr and triggers scan ioapic logic to load synic vectors into EOI exit bitmap. However, irqchip is not initialized by this simple testcase, ioapic/apic objects should not be accessed. This can be triggered by the following program: #define _GNU_SOURCE #include <endian.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/syscall.h> #include <sys/types.h> #include <unistd.h> uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff}; int main(void) { syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0); long res = 0; memcpy((void*)0x20000040, "/dev/kvm", 9); res = syscall(__NR_openat, 0xffffffffffffff9c, 0x20000040, 0, 0); if (res != -1) r[0] = res; res = syscall(__NR_ioctl, r[0], 0xae01, 0); if (res != -1) r[1] = res; res = syscall(__NR_ioctl, r[1], 0xae41, 0); if (res != -1) r[2] = res; memcpy( (void*)0x20000080, "\x01\x00\x00\x00\x00\x5b\x61\xbb\x96\x00\x00\x40\x00\x00\x00\x00\x01\x00" "\x08\x00\x00\x00\x00\x00\x0b\x77\xd1\x78\x4d\xd8\x3a\xed\xb1\x5c\x2e\x43" "\xaa\x43\x39\xd6\xff\xf5\xf0\xa8\x98\xf2\x3e\x37\x29\x89\xde\x88\xc6\x33" "\xfc\x2a\xdb\xb7\xe1\x4c\xac\x28\x61\x7b\x9c\xa9\xbc\x0d\xa0\x63\xfe\xfe" "\xe8\x75\xde\xdd\x19\x38\xdc\x34\xf5\xec\x05\xfd\xeb\x5d\xed\x2e\xaf\x22" "\xfa\xab\xb7\xe4\x42\x67\xd0\xaf\x06\x1c\x6a\x35\x67\x10\x55\xcb", 106); syscall(__NR_ioctl, r[2], 0x4008ae89, 0x20000080); syscall(__NR_ioctl, r[2], 0xae80, 0); return 0; } This patch fixes it by bailing out scan ioapic if ioapic is not initialized in kernel. Reported-by:
Wei Wu <ww9210@gmail.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Wei Wu <ww9210@gmail.com> Signed-off-by:
Wanpeng Li <wanpengli@tencent.com> Cc: stable@vger.kernel.org Signed-off-by:
Paolo Bonzini <pbonzini@redhat.com> Signed-off-by:
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Liran Alon authored
commit bcbfbd8e upstream. kvm_pv_clock_pairing() allocates local var "struct kvm_clock_pairing clock_pairing" on stack and initializes all it's fields besides padding (clock_pairing.pad[]). Because clock_pairing var is written completely (including padding) to guest memory, failure to init struct padding results in kernel info-leak. Fix the issue by making sure to also init the padding with zeroes. Fixes: 55dd00a7 ("KVM: x86: add KVM_HC_CLOCK_PAIRING hypercall") Reported-by: syzbot+a8ef68d71211ba264f56@syzkaller.appspotmail.com Reviewed-by:
Mark Kanda <mark.kanda@oracle.com> Signed-off-by:
Liran Alon <liran.alon@oracle.com> Cc: stable@vger.kernel.org Signed-off-by:
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Jim Mattson authored
commit fd65d314 upstream. Previously, we only called indirect_branch_prediction_barrier on the logical CPU that freed a vmcb. This function should be called on all logical CPUs that last loaded the vmcb in question. Fixes: 15d45071 ("KVM/x86: Add IBPB support") Reported-by:
Neel Natu <neelnatu@google.com> Signed-off-by:
Jim Mattson <jmattson@google.com> Reviewed-by:
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: stable@vger.kernel.org Signed-off-by:
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Junaid Shahid authored
commit 0e0fee5c upstream. When a guest page table is updated via an emulated write, kvm_mmu_pte_write() is called to update the shadow PTE using the just written guest PTE value. But if two emulated guest PTE writes happened concurrently, it is possible that the guest PTE and the shadow PTE end up being out of sync. Emulated writes do not mark the shadow page as unsync-ed, so this inconsistency will not be resolved even by a guest TLB flush (unless the page was marked as unsync-ed at some other point). This is fixed by re-reading the current value of the guest PTE after the MMU lock has been acquired instead of just using the value that was written prior to calling kvm_mmu_pte_write(). Signed-off-by:
Junaid Shahid <junaids@google.com> Reviewed-by:
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Thomas Gleixner authored
commit 55a97402 upstream Provide the possibility to enable IBPB always in combination with 'prctl' and 'seccomp'. Add the extra command line options and rework the IBPB selection to evaluate the command instead of the mode selected by the STIPB switch case. Signed-off-by:
Thomas Gleixner <tglx@linutronix.de> Reviewed-by:
Ingo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Woodhouse <dwmw@amazon.co.uk> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Casey Schaufler <casey.schaufler@intel.com> Cc: Asit Mallick <asit.k.mallick@intel.com> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Jon Masters <jcm@redhat.com> Cc: Waiman Long <longman9394@gmail.com> Cc: Greg KH <gregkh@linuxfoundation.org> Cc: Dave Stewart <david.c.stewart@intel.com> Cc: Kees Cook <keescook@chromium.org> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20181125185006.144047038@linutronix.deSigned-off-by:
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Thomas Gleixner authored
commit 6b3e64c2 upstream If 'prctl' mode of user space protection from spectre v2 is selected on the kernel command-line, STIBP and IBPB are applied on tasks which restrict their indirect branch speculation via prctl. SECCOMP enables the SSBD mitigation for sandboxed tasks already, so it makes sense to prevent spectre v2 user space to user space attacks as well. The Intel mitigation guide documents how STIPB works: Setting bit 1 (STIBP) of the IA32_SPEC_CTRL MSR on a logical processor prevents the predicted targets of indirect branches on any logical processor of that core from being controlled by software that executes (or executed previously) on another logical processor of the same core. Ergo setting STIBP protects the task itself from being attacked from a task running on a different hyper-thread and protects the tasks running on different hyper-threads from being attacked. While the document suggests that the branch predictors are shielded between the logical processors, the observed performance regressions suggest that STIBP simply disables the branch predictor more or less completely. Of course the document wording is vague, but the fact that there is also no requirement for issuing IBPB when STIBP is used points clearly in that direction. The kernel still issues IBPB even when STIBP is used until Intel clarifies the whole mechanism. IBPB is issued when the task switches out, so malicious sandbox code cannot mistrain the branch predictor for the next user space task on the same logical processor. Signed-off-by:
Jiri Kosina <jkosina@suse.cz> Signed-off-by:
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Thomas Gleixner authored
commit 7cc765a6 upstream Now that all prerequisites are in place: - Add the prctl command line option - Default the 'auto' mode to 'prctl' - When SMT state changes, update the static key which controls the conditional STIBP evaluation on context switch. - At init update the static key which controls the conditional IBPB evaluation on context switch. Signed-off-by:
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Thomas Gleixner authored
commit 9137bb27 upstream Add the PR_SPEC_INDIRECT_BRANCH option for the PR_GET_SPECULATION_CTRL and PR_SET_SPECULATION_CTRL prctls to allow fine grained per task control of indirect branch speculation via STIBP and IBPB. Invocations: Check indirect branch speculation status with - prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, 0, 0, 0); Enable indirect branch speculation with - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_ENABLE, 0, 0); Disable indirect branch speculation with - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_DISABLE, 0, 0); Force disable indirect branch speculation with - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0); See Documentation/userspace-api/spec_ctrl.rst. Signed-off-by:
Tim Chen <tim.c.chen@linux.intel.com> Signed-off-by:
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Thomas Gleixner authored
commit 6893a959 upstream The upcoming fine grained per task STIBP control needs to be updated on CPU hotplug as well. Split out the code which controls the strict mode so the prctl control code can be added later. Mark the SMP function call argument __unused while at it. Signed-off-by:
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Thomas Gleixner authored
commit 6d991ba5 upstream The seccomp speculation control operates on all tasks of a process, but only the current task of a process can update the MSR immediately. For the other threads the update is deferred to the next context switch. This creates the following situation with Process A and B: Process A task 2 and Process B task 1 are pinned on CPU1. Process A task 2 does not have the speculation control TIF bit set. Process B task 1 has the speculation control TIF bit set. CPU0 CPU1 MSR bit is set ProcB.T1 schedules out ProcA.T2 schedules in MSR bit is cleared ProcA.T1 seccomp_update() set TIF bit on ProcA.T2 ProcB.T1 schedules in MSR is not updated <-- FAIL This happens because the context switch code tries to avoid the MSR update if the speculation control TIF bits of the incoming and the outgoing task are the same. In the worst case ProcB.T1 and ProcA.T2 are the only tasks scheduling back and forth on CPU1, which keeps the MSR stale forever. In theory this could be remedied by IPIs, but chasing the remote task which could be migrated is complex and full of races. The straight forward solution is to avoid the asychronous update of the TIF bit and defer it to the next context switch. The speculation control state is stored in task_struct::atomic_flags by the prctl and seccomp updates already. Add a new TIF_SPEC_FORCE_UPDATE bit and set this after updating the atomic_flags. Check the bit on context switch and force a synchronous update of the speculation control if set. Use the same mechanism for updating the current task. Reported-by:
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Thomas Gleixner authored
commit e6da8bb6 upstream The update of the TIF_SSBD flag and the conditional speculation control MSR update is done in the ssb_prctl_set() function directly. The upcoming prctl support for controlling indirect branch speculation via STIBP needs the same mechanism. Split the code out and make it reusable. Reword the comment about updates for other tasks. Signed-off-by:
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Thomas Gleixner authored
commit 46f7ecb1 upstream The IBPB control code in x86 removed the usage. Remove the functionality which was introduced for this. Signed-off-by:
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Thomas Gleixner authored
commit 4c71a2b6 upstream The IBPB speculation barrier is issued from switch_mm() when the kernel switches to a user space task with a different mm than the user space task which ran last on the same CPU. An additional optimization is to avoid IBPB when the incoming task can be ptraced by the outgoing task. This optimization only works when switching directly between two user space tasks. When switching from a kernel task to a user space task the optimization fails because the previous task cannot be accessed anymore. So for quite some scenarios the optimization is just adding overhead. The upcoming conditional IBPB support will issue IBPB only for user space tasks which have the TIF_SPEC_IB bit set. This requires to handle the following cases: 1) Switch from a user space task (potential attacker) which has TIF_SPEC_IB set to a user space task (potential victim) which has TIF_SPEC_IB not set. 2) Switch from a user space task (potential attacker) which has TIF_SPEC_IB not set to a user space task (potential victim) which has TIF_SPEC_IB set. This needs to be optimized for the case where the IBPB can be avoided when only kernel threads ran in between user space tasks which belong to the same process. The current check whether two tasks belong to the same context is using the tasks context id. While correct, it's simpler to use the mm pointer because it allows to mangle the TIF_SPEC_IB bit into it. The context id based mechanism requires extra storage, which creates worse code. When a task is scheduled out its TIF_SPEC_IB bit is mangled as bit 0 into the per CPU storage which is used to track the last user space mm which was running on a CPU. This bit can be used together with the TIF_SPEC_IB bit of the incoming task to make the decision whether IBPB needs to be issued or not to cover the two cases above. As conditional IBPB is going to be the default, remove the dubious ptrace check for the IBPB always case and simply issue IBPB always when the process changes. Move the storage to a different place in the struct as the original one created a hole. Signed-off-by:
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Thomas Gleixner authored
commit 5635d999 upstream The TIF_SPEC_IB bit does not need to be evaluated in the decision to invoke __switch_to_xtra() when: - CONFIG_SMP is disabled - The conditional STIPB mode is disabled The TIF_SPEC_IB bit still controls IBPB in both cases so the TIF work mask checks might invoke __switch_to_xtra() for nothing if TIF_SPEC_IB is the only set bit in the work masks. Optimize it out by masking the bit at compile time for CONFIG_SMP=n and at run time when the static key controlling the conditional STIBP mode is disabled. Signed-off-by:
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Thomas Gleixner authored
commit ff16701a upstream Move the conditional invocation of __switch_to_xtra() into an inline function so the logic can be shared between 32 and 64 bit. Remove the handthrough of the TSS pointer and retrieve the pointer directly in the bitmap handling function. Use this_cpu_ptr() instead of the per_cpu() indirection. This is a preparatory change so integration of conditional indirect branch speculation optimization happens only in one place. Signed-off-by:
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Tim Chen authored
commit 5bfbe3ad upstream To avoid the overhead of STIBP always on, it's necessary to allow per task control of STIBP. Add a new task flag TIF_SPEC_IB and evaluate it during context switch if SMT is active and flag evaluation is enabled by the speculation control code. Add the conditional evaluation to x86_virt_spec_ctrl() as well so the guest/host switch works properly. This has no effect because TIF_SPEC_IB cannot be set yet and the static key which controls evaluation is off. Preparatory patch for adding the control code. [ tglx: Simplify the context switch logic and make the TIF evaluation depend on SMP=y and on the static key controlling the conditional update. Rename it to TIF_SPEC_IB because it controls both STIBP and IBPB ] Signed-off-by:
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Thomas Gleixner authored
commit fa1202ef upstream Add command line control for user space indirect branch speculation mitigations. The new option is: spectre_v2_user= The initial options are: - on: Unconditionally enabled - off: Unconditionally disabled -auto: Kernel selects mitigation (default off for now) When the spectre_v2= command line argument is either 'on' or 'off' this implies that the application to application control follows that state even if a contradicting spectre_v2_user= argument is supplied. Originally-by:
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Thomas Gleixner authored
commit 495d470e upstream There is no point in having two functions and a conditional at the call site. Signed-off-by:
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Thomas Gleixner authored
commit 30ba72a9 upstream No point to keep that around. Signed-off-by:
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Thomas Gleixner authored
commit 8770709f upstream checkpatch.pl muttered when reshuffling the code: WARNING: static const char * array should probably be static const char * const Fix up all the string arrays. Signed-off-by:
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Thomas Gleixner authored
commit 15d6b7aa upstream Reorder the code so it is better grouped. No functional change. Signed-off-by:
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Thomas Gleixner authored
commit 130d6f94 upstream Use the now exposed real SMT state, not the SMT sysfs control knob state. This reflects the state of the system when the mitigation status is queried. This does not change the warning in the VMX launch code. There the dependency on the control knob makes sense because siblings could be brought online anytime after launching the VM. Signed-off-by:
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Thomas Gleixner authored
commit a74cfffb upstream arch_smt_update() is only called when the sysfs SMT control knob is changed. This means that when SMT is enabled in the sysfs control knob the system is considered to have SMT active even if all siblings are offline. To allow finegrained control of the speculation mitigations, the actual SMT state is more interesting than the fact that siblings could be enabled. Rework the code, so arch_smt_update() is invoked from each individual CPU hotplug function, and simplify the update function while at it. Signed-off-by:
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Thomas Gleixner authored
commit 321a874a upstream Make the scheduler's 'sched_smt_present' static key globaly available, so it can be used in the x86 speculation control code. Provide a query function and a stub for the CONFIG_SMP=n case. Signed-off-by:
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Thomas Gleixner authored
commit dbe73364 upstream CONFIG_SCHED_SMT is enabled by all distros, so there is not a real point to have it configurable. The runtime overhead in the core scheduler code is minimal because the actual SMT scheduling parts are conditional on a static key. This allows to expose the scheduler's SMT state static key to the speculation control code. Alternatively the scheduler's static key could be made always available when CONFIG_SMP is enabled, but that's just adding an unused static key to every other architecture for nothing. Signed-off-by:
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Peter Zijlstra (Intel) authored
commit c5511d03 upstream Currently the 'sched_smt_present' static key is enabled when at CPU bringup SMT topology is observed, but it is never disabled. However there is demand to also disable the key when the topology changes such that there is no SMT present anymore. Implement this by making the key count the number of cores that have SMT enabled. In particular, the SMT topology bits are set before interrrupts are enabled and similarly, are cleared after interrupts are disabled for the last time and the CPU dies. Signed-off-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by:
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Tim Chen authored
commit 01daf568 upstream The logic to detect whether there's a change in the previous and next task's flag relevant to update speculation control MSRs is spread out across multiple functions. Consolidate all checks needed for updating speculation control MSRs into the new __speculation_ctrl_update() helper function. This makes it easy to pick the right speculation control MSR and the bits in MSR_IA32_SPEC_CTRL that need updating based on TIF flags changes. Originally-by:
Thomas Lendacky <Thomas.Lendacky@amd.com> Signed-off-by:
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Thomas Gleixner authored
commit 26c4d75b upstream During context switch, the SSBD bit in SPEC_CTRL MSR is updated according to changes of the TIF_SSBD flag in the current and next running task. Currently, only the bit controlling speculative store bypass disable in SPEC_CTRL MSR is updated and the related update functions all have "speculative_store" or "ssb" in their names. For enhanced mitigation control other bits in SPEC_CTRL MSR need to be updated as well, which makes the SSB names inadequate. Rename the "speculative_store*" functions to a more generic name. No functional change. Signed-off-by:
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Tim Chen authored
commit 34bce7c9 upstream If enhanced IBRS is active, STIBP is redundant for mitigating Spectre v2 user space exploits from hyperthread sibling. Disable STIBP when enhanced IBRS is used. Signed-off-by:
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Tim Chen authored
commit a8f76ae4 upstream The Spectre V2 printout in cpu_show_common() handles conditionals for the various mitigation methods directly in the sprintf() argument list. That's hard to read and will become unreadable if more complex decisions need to be made for a particular method. Move the conditionals for STIBP and IBPB string selection into helper functions, so they can be extended later on. Signed-off-by:
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Tim Chen authored
commit b86bda04 upstream Signed-off-by:
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Tim Chen authored
commit 24848509 upstream Remove the unnecessary 'else' statement in spectre_v2_parse_cmdline() to save an indentation level. Signed-off-by:
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Tim Chen authored
commit 8eb729b7 upstream "Reduced Data Speculation" is an obsolete term. The correct new name is "Speculative store bypass disable" - which is abbreviated into SSBD. Signed-off-by:
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Zhenzhong Duan authored
commit ef014aae upstream Now that CONFIG_RETPOLINE hard depends on compiler support, there is no reason to keep the minimal retpoline support around which only provided basic protection in the assembly files. Suggested-by:
Zhenzhong Duan <zhenzhong.duan@oracle.com> Signed-off-by:
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Zhenzhong Duan authored
commit 4cd24de3 upstream Since retpoline capable compilers are widely available, make CONFIG_RETPOLINE hard depend on the compiler capability. Break the build when CONFIG_RETPOLINE is enabled and the compiler does not support it. Emit an error message in that case: "arch/x86/Makefile:226: *** You are building kernel with non-retpoline compiler, please update your compiler.. Stop." [dwmw: Fail the build with non-retpoline compiler] Suggested-by:
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Zhenzhong Duan authored
commit 0cbb76d6 upstream ..so that they match their asm counterpart. Add the missing ANNOTATE_NOSPEC_ALTERNATIVE in CALL_NOSPEC, while at it. Signed-off-by:
Borislav Petkov <bp@suse.de> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: David Woodhouse <dwmw@amazon.co.uk> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Wang YanQing <udknight@gmail.com> Cc: dhaval.giani@oracle.com Cc: srinivas.eeda@oracle.com Link: http://lkml.kernel.org/r/c3975665-173e-4d70-8dee-06c926ac26ee@defaultSigned-off-by:
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Jiri Kosina authored
commit bb4b3b77 upstream If spectrev2 mitigation has been enabled, RSB is filled on context switch in order to protect from various classes of spectrev2 attacks. If this mitigation is enabled, say so in sysfs for spectrev2. Signed-off-by:
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Jiri Kosina authored
commit dbfe2953 upstream Currently, IBPB is only issued in cases when switching into a non-dumpable process, the rationale being to protect such 'important and security sensitive' processess (such as GPG) from data leaking into a different userspace process via spectre v2. This is however completely insufficient to provide proper userspace-to-userpace spectrev2 protection, as any process can poison branch buffers before being scheduled out, and the newly scheduled process immediately becomes spectrev2 victim. In order to minimize the performance impact (for usecases that do require spectrev2 protection), issue the barrier only in cases when switching between processess where the victim can't be ptraced by the potential attacker (as in such cases, the attacker doesn't have to bother with branch buffers at all). [ tglx: Split up PTRACE_MODE_NOACCESS_CHK into PTRACE_MODE_SCHED and PTRACE_MODE_IBPB to be able to do ptrace() context tracking reasonably fine-grained ] Fixes: 18bf3c3e ("x86/speculation: Use Indirect Branch Prediction Barrier in context switch") Originally-by:
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