Commit f17c4e01 authored by Michael Ellerman's avatar Michael Ellerman

powerpc/module: Mark module stubs with a magic value

When a module is loaded, calls out to the kernel go via a stub which is
generated at runtime. One of these stubs is used to call _mcount(),
which is the default target of tracing calls generated by the compiler
with -pg.

If dynamic ftrace is enabled (which it typically is), another stub is
used to call ftrace_caller(), which is the target of tracing calls when
ftrace is actually active.

ftrace then wants to disable the calls to _mcount() at module startup,
and enable/disable the calls to ftrace_caller() when enabling/disabling
tracing - all of these it does by patching the code.

As part of that code patching, the ftrace code wants to confirm that the
branch it is about to modify, is in fact a call to a module stub which
calls _mcount() or ftrace_caller().

Currently it does that by inspecting the instructions and confirming
they are what it expects. Although that works, the code to do it is
pretty intricate because it requires lots of knowledge about the exact
format of the stub.

We can make that process easier by marking the generated stubs with a
magic value, and then looking for that magic value. Altough this is not
as rigorous as the current method, I believe it is sufficient in
practice.
Reviewed-by: default avatarBalbir Singh <bsingharora@gmail.com>
Reviewed-by: default avatarTorsten Duwe <duwe@suse.de>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 136cd345
...@@ -78,8 +78,7 @@ struct mod_arch_specific { ...@@ -78,8 +78,7 @@ struct mod_arch_specific {
# endif /* MODULE */ # endif /* MODULE */
#endif #endif
bool is_module_trampoline(u32 *insns); int module_trampoline_target(struct module *mod, unsigned long trampoline,
int module_trampoline_target(struct module *mod, u32 *trampoline,
unsigned long *target); unsigned long *target);
#ifdef CONFIG_DYNAMIC_FTRACE #ifdef CONFIG_DYNAMIC_FTRACE
......
...@@ -106,10 +106,9 @@ static int ...@@ -106,10 +106,9 @@ static int
__ftrace_make_nop(struct module *mod, __ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr) struct dyn_ftrace *rec, unsigned long addr)
{ {
unsigned int op; unsigned long entry, ptr, tramp;
unsigned long entry, ptr;
unsigned long ip = rec->ip; unsigned long ip = rec->ip;
void *tramp; unsigned int op;
/* read where this goes */ /* read where this goes */
if (probe_kernel_read(&op, (void *)ip, sizeof(int))) if (probe_kernel_read(&op, (void *)ip, sizeof(int)))
...@@ -122,14 +121,9 @@ __ftrace_make_nop(struct module *mod, ...@@ -122,14 +121,9 @@ __ftrace_make_nop(struct module *mod,
} }
/* lets find where the pointer goes */ /* lets find where the pointer goes */
tramp = (void *)find_bl_target(ip, op); tramp = find_bl_target(ip, op);
pr_devel("ip:%lx jumps to %p", ip, tramp);
if (!is_module_trampoline(tramp)) { pr_devel("ip:%lx jumps to %lx", ip, tramp);
pr_err("Not a trampoline\n");
return -EINVAL;
}
if (module_trampoline_target(mod, tramp, &ptr)) { if (module_trampoline_target(mod, tramp, &ptr)) {
pr_err("Failed to get trampoline target\n"); pr_err("Failed to get trampoline target\n");
......
...@@ -96,6 +96,8 @@ static unsigned int local_entry_offset(const Elf64_Sym *sym) ...@@ -96,6 +96,8 @@ static unsigned int local_entry_offset(const Elf64_Sym *sym)
} }
#endif #endif
#define STUB_MAGIC 0x73747562 /* stub */
/* Like PPC32, we need little trampolines to do > 24-bit jumps (into /* Like PPC32, we need little trampolines to do > 24-bit jumps (into
the kernel itself). But on PPC64, these need to be used for every the kernel itself). But on PPC64, these need to be used for every
jump, actually, to reset r2 (TOC+0x8000). */ jump, actually, to reset r2 (TOC+0x8000). */
...@@ -105,7 +107,8 @@ struct ppc64_stub_entry ...@@ -105,7 +107,8 @@ struct ppc64_stub_entry
* need 6 instructions on ABIv2 but we always allocate 7 so * need 6 instructions on ABIv2 but we always allocate 7 so
* so we don't have to modify the trampoline load instruction. */ * so we don't have to modify the trampoline load instruction. */
u32 jump[7]; u32 jump[7];
u32 unused; /* Used by ftrace to identify stubs */
u32 magic;
/* Data for the above code */ /* Data for the above code */
func_desc_t funcdata; func_desc_t funcdata;
}; };
...@@ -139,70 +142,39 @@ static u32 ppc64_stub_insns[] = { ...@@ -139,70 +142,39 @@ static u32 ppc64_stub_insns[] = {
}; };
#ifdef CONFIG_DYNAMIC_FTRACE #ifdef CONFIG_DYNAMIC_FTRACE
int module_trampoline_target(struct module *mod, unsigned long addr,
static u32 ppc64_stub_mask[] = { unsigned long *target)
0xffff0000,
0xffff0000,
0xffffffff,
0xffffffff,
#if !defined(_CALL_ELF) || _CALL_ELF != 2
0xffffffff,
#endif
0xffffffff,
0xffffffff
};
bool is_module_trampoline(u32 *p)
{ {
unsigned int i; struct ppc64_stub_entry *stub;
u32 insns[ARRAY_SIZE(ppc64_stub_insns)]; func_desc_t funcdata;
u32 magic;
BUILD_BUG_ON(sizeof(ppc64_stub_insns) != sizeof(ppc64_stub_mask));
if (probe_kernel_read(insns, p, sizeof(insns))) if (!within_module_core(addr, mod)) {
pr_err("%s: stub %lx not in module %s\n", __func__, addr, mod->name);
return -EFAULT; return -EFAULT;
for (i = 0; i < ARRAY_SIZE(ppc64_stub_insns); i++) {
u32 insna = insns[i];
u32 insnb = ppc64_stub_insns[i];
u32 mask = ppc64_stub_mask[i];
if ((insna & mask) != (insnb & mask))
return false;
} }
return true; stub = (struct ppc64_stub_entry *)addr;
}
int module_trampoline_target(struct module *mod, u32 *trampoline, if (probe_kernel_read(&magic, &stub->magic, sizeof(magic))) {
unsigned long *target) pr_err("%s: fault reading magic for stub %lx for %s\n", __func__, addr, mod->name);
{
u32 buf[2];
u16 upper, lower;
long offset;
void *toc_entry;
if (probe_kernel_read(buf, trampoline, sizeof(buf)))
return -EFAULT; return -EFAULT;
}
upper = buf[0] & 0xffff; if (magic != STUB_MAGIC) {
lower = buf[1] & 0xffff; pr_err("%s: bad magic for stub %lx for %s\n", __func__, addr, mod->name);
return -EFAULT;
/* perform the addis/addi, both signed */ }
offset = ((short)upper << 16) + (short)lower;
/*
* Now get the address this trampoline jumps to. This
* is always 32 bytes into our trampoline stub.
*/
toc_entry = (void *)mod->arch.toc + offset + 32;
if (probe_kernel_read(target, toc_entry, sizeof(*target))) if (probe_kernel_read(&funcdata, &stub->funcdata, sizeof(funcdata))) {
pr_err("%s: fault reading funcdata for stub %lx for %s\n", __func__, addr, mod->name);
return -EFAULT; return -EFAULT;
}
*target = stub_func_addr(funcdata);
return 0; return 0;
} }
#endif #endif
/* Count how many different 24-bit relocations (different symbol, /* Count how many different 24-bit relocations (different symbol,
...@@ -447,6 +419,8 @@ static inline int create_stub(const Elf64_Shdr *sechdrs, ...@@ -447,6 +419,8 @@ static inline int create_stub(const Elf64_Shdr *sechdrs,
entry->jump[0] |= PPC_HA(reladdr); entry->jump[0] |= PPC_HA(reladdr);
entry->jump[1] |= PPC_LO(reladdr); entry->jump[1] |= PPC_LO(reladdr);
entry->funcdata = func_desc(addr); entry->funcdata = func_desc(addr);
entry->magic = STUB_MAGIC;
return 1; return 1;
} }
......
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