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authorOleg Nesterov <oleg@redhat.com>2015-07-21 16:40:28 +0300
committerIngo Molnar <mingo@kernel.org>2015-07-31 11:38:06 +0300
commitdb087ef69a2b155ae001665bf0b3806abde7ee34 (patch)
tree2f9837a9c4323692ca2702e72de7f253331da8d9 /arch/x86/kernel/uprobes.c
parent86dcb702e74b8ab7d3b2d36984ef00671cea73b9 (diff)
downloadlinux-db087ef69a2b155ae001665bf0b3806abde7ee34.tar.xz
uprobes/x86: Make arch_uretprobe_is_alive(RP_CHECK_CALL) more clever
The previous change documents that cleanup_return_instances() can't always detect the dead frames, the stack can grow. But there is one special case which imho worth fixing: arch_uretprobe_is_alive() can return true when the stack didn't actually grow, but the next "call" insn uses the already invalidated frame. Test-case: #include <stdio.h> #include <setjmp.h> jmp_buf jmp; int nr = 1024; void func_2(void) { if (--nr == 0) return; longjmp(jmp, 1); } void func_1(void) { setjmp(jmp); func_2(); } int main(void) { func_1(); return 0; } If you ret-probe func_1() and func_2() prepare_uretprobe() hits the MAX_URETPROBE_DEPTH limit and "return" from func_2() is not reported. When we know that the new call is not chained, we can do the more strict check. In this case "sp" points to the new ret-addr, so every frame which uses the same "sp" must be dead. The only complication is that arch_uretprobe_is_alive() needs to know was it chained or not, so we add the new RP_CHECK_CHAIN_CALL enum and change prepare_uretprobe() to pass RP_CHECK_CALL only if !chained. Note: arch_uretprobe_is_alive() could also re-read *sp and check if this word is still trampoline_vaddr. This could obviously improve the logic, but I would like to avoid another copy_from_user() especially in the case when we can't avoid the false "alive == T" positives. Tested-by: Pratyush Anand <panand@redhat.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Acked-by: Anton Arapov <arapov@gmail.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20150721134028.GA4786@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/uprobes.c')
-rw-r--r--arch/x86/kernel/uprobes.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index acf8b9010bbf..bf4db6eaec8f 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -989,5 +989,8 @@ arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs
bool arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx,
struct pt_regs *regs)
{
- return regs->sp <= ret->stack;
+ if (ctx == RP_CHECK_CALL) /* sp was just decremented by "call" insn */
+ return regs->sp < ret->stack;
+ else
+ return regs->sp <= ret->stack;
}