Messages in this thread Patch in this message | | | From | Chen Zhongjin <> | Subject | [PATCH v2] x86: profiling: remove lock functions hack for !FRAME_POINTER | Date | Thu, 13 Apr 2023 15:37:56 +0800 |
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Syzbot has been reporting the problem of stack-out-of-bounds in profile_pc for a long time: https://syzkaller.appspot.com/bug?extid=84fe685c02cd112a2ac3
profile_pc will get return address for caller if current function is lock function. For !CONFIG_FRAME_POINTER it uses a hack way to get the caller by directly reading sp[0] or sp [1]. It not works when KASAN is enabled because KASAN pushes data on stack which makes sp[0/1] become KASAN red zone. Then profile_pc reads wrong memory and triggers KASAN warning frequently.
This hack might be ok when first added at 2006 but now it's different:
1. There are some lock functions which have frame longer than two stack slots. For these functions sp[0/1] is not a legal return address even KASAN is not enabled. 2. !CONFIG_FRAME_POINTER is more used today because UNWINDER_ORC. 3. Lock function caller information can be prfiled by perf better.
Since profile as a low level facility it's better not to depend on complex generic unwinder to get the next frame. So it's reasonable to remove lock functions hack for !FRAME_POINTER kernel.
Fixes: 0cb91a229364 ("[PATCH] i386: Account spinlocks to the caller during profiling for !FP kernels") Suggested-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com> --- v1->v2: Make a more detailed commit log. --- arch/x86/kernel/time.c | 14 +------------- 1 file changed, 1 insertion(+), 13 deletions(-)
diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c index e42faa792c07..e08fac7bb71e 100644 --- a/arch/x86/kernel/time.c +++ b/arch/x86/kernel/time.c @@ -29,22 +29,10 @@ unsigned long profile_pc(struct pt_regs *regs) { unsigned long pc = instruction_pointer(regs); - if (!user_mode(regs) && in_lock_functions(pc)) { #ifdef CONFIG_FRAME_POINTER + if (!user_mode(regs) && in_lock_functions(pc)) return *(unsigned long *)(regs->bp + sizeof(long)); -#else - unsigned long *sp = (unsigned long *)regs->sp; - /* - * Return address is either directly at stack pointer - * or above a saved flags. Eflags has bits 22-31 zero, - * kernel addresses don't. - */ - if (sp[0] >> 22) - return sp[0]; - if (sp[1] >> 22) - return sp[1]; #endif - } return pc; } EXPORT_SYMBOL(profile_pc); -- 2.17.1
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