From 9254139ad083433c50ba62920107ed55fc4ca5e2 Mon Sep 17 00:00:00 2001 From: Dmitry Vyukov Date: Tue, 11 Oct 2016 14:13:38 +0200 Subject: [PATCH] kprobes: Avoid false KASAN reports during stack copy Kprobes save and restore raw stack chunks with memcpy(). With KASAN these chunks can contain poisoned stack redzones, as the result memcpy() interceptor produces false stack out-of-bounds reports. Use __memcpy() instead of memcpy() for stack copying. __memcpy() is not instrumented by KASAN and does not lead to the false reports. Currently there is a spew of KASAN reports during boot if CONFIG_KPROBES_SANITY_TEST is enabled: [ ] Kprobe smoke test: started [ ] ================================================================== [ ] BUG: KASAN: stack-out-of-bounds in setjmp_pre_handler+0x17c/0x280 at addr ffff88085259fba8 [ ] Read of size 64 by task swapper/0/1 [ ] page:ffffea00214967c0 count:0 mapcount:0 mapping: (null) index:0x0 [ ] flags: 0x2fffff80000000() [ ] page dumped because: kasan: bad access detected [...] Reported-by: CAI Qian Tested-by: CAI Qian Signed-off-by: Dmitry Vyukov Acked-by: Masami Hiramatsu Cc: Alexander Potapenko Cc: Alexander Shishkin Cc: Ananth N Mavinakayanahalli Cc: Andrew Morton Cc: Andrey Ryabinin Cc: Andy Lutomirski Cc: Anil S Keshavamurthy Cc: Arnaldo Carvalho de Melo Cc: Borislav Petkov Cc: Brian Gerst Cc: David S. Miller Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Jiri Olsa Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: kasan-dev@googlegroups.com [ Improved various details. ] Signed-off-by: Ingo Molnar --- arch/x86/kernel/kprobes/core.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c index 28cee019209c..f423b0ef23a7 100644 --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -1057,9 +1057,10 @@ int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs) * tailcall optimization. So, to be absolutely safe * we also save and restore enough stack bytes to cover * the argument area. + * Use __memcpy() to avoid KASAN stack out-of-bounds reports as we copy + * raw stack chunk with redzones: */ - memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr, - MIN_STACK_SIZE(addr)); + __memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr, MIN_STACK_SIZE(addr)); regs->flags &= ~X86_EFLAGS_IF; trace_hardirqs_off(); regs->ip = (unsigned long)(jp->entry); @@ -1118,7 +1119,7 @@ int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) /* It's OK to start function graph tracing again */ unpause_graph_tracing(); *regs = kcb->jprobe_saved_regs; - memcpy(saved_sp, kcb->jprobes_stack, MIN_STACK_SIZE(saved_sp)); + __memcpy(saved_sp, kcb->jprobes_stack, MIN_STACK_SIZE(saved_sp)); preempt_enable_no_resched(); return 1; }