From b0d50c7b5d807ce6f7ba58e42b260e92bd7d88fb Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Tue, 25 Apr 2017 20:48:51 -0500 Subject: [PATCH] x86/unwind: Silence more entry-code related warnings Borislav Petkov reported the following unwinder warning: WARNING: kernel stack regs at ffffc9000024fea8 in udevadm:92 has bad 'bp' value 00007fffc4614d30 unwind stack type:0 next_sp: (null) mask:0x6 graph_idx:0 ffffc9000024fea8: 000055a6100e9b38 (0x55a6100e9b38) ffffc9000024feb0: 000055a6100e9b35 (0x55a6100e9b35) ffffc9000024feb8: 000055a6100e9f68 (0x55a6100e9f68) ffffc9000024fec0: 000055a6100e9f50 (0x55a6100e9f50) ffffc9000024fec8: 00007fffc4614d30 (0x7fffc4614d30) ffffc9000024fed0: 000055a6100eaf50 (0x55a6100eaf50) ffffc9000024fed8: 0000000000000000 ... ffffc9000024fee0: 0000000000000100 (0x100) ffffc9000024fee8: ffff8801187df488 (0xffff8801187df488) ffffc9000024fef0: 00007ffffffff000 (0x7ffffffff000) ffffc9000024fef8: 0000000000000000 ... ffffc9000024ff10: ffffc9000024fe98 (0xffffc9000024fe98) ffffc9000024ff18: 00007fffc4614d00 (0x7fffc4614d00) ffffc9000024ff20: ffffffffffffff10 (0xffffffffffffff10) ffffc9000024ff28: ffffffff811c6c1f (SyS_newlstat+0xf/0x10) ffffc9000024ff30: 0000000000000010 (0x10) ffffc9000024ff38: 0000000000000296 (0x296) ffffc9000024ff40: ffffc9000024ff50 (0xffffc9000024ff50) ffffc9000024ff48: 0000000000000018 (0x18) ffffc9000024ff50: ffffffff816b2e6a (entry_SYSCALL_64_fastpath+0x18/0xa8) ... It unwinded from an interrupt which came in right after entry code called into a C syscall handler, before it had a chance to set up the frame pointer, so regs->bp still had its user space value. Add a check to silence warnings in such a case, where an interrupt has occurred and regs->sp is almost at the end of the stack. Reported-by: Borislav Petkov Tested-by: Borislav Petkov Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: c32c47c68a0a ("x86/unwind: Warn on bad frame pointer") Link: http://lkml.kernel.org/r/c695f0d0d4c2cfe6542b90e2d0520e11eb901eb5.1493171120.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/unwind_frame.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c index bda82df34c7b..ae0821f6c3a5 100644 --- a/arch/x86/kernel/unwind_frame.c +++ b/arch/x86/kernel/unwind_frame.c @@ -91,16 +91,26 @@ static bool in_entry_code(unsigned long ip) return false; } +static inline unsigned long *last_frame(struct unwind_state *state) +{ + return (unsigned long *)task_pt_regs(state->task) - 2; +} + #ifdef CONFIG_X86_32 #define GCC_REALIGN_WORDS 3 #else #define GCC_REALIGN_WORDS 1 #endif +static inline unsigned long *last_aligned_frame(struct unwind_state *state) +{ + return last_frame(state) - GCC_REALIGN_WORDS; +} + static bool is_last_task_frame(struct unwind_state *state) { - unsigned long *last_bp = (unsigned long *)task_pt_regs(state->task) - 2; - unsigned long *aligned_bp = last_bp - GCC_REALIGN_WORDS; + unsigned long *last_bp = last_frame(state); + unsigned long *aligned_bp = last_aligned_frame(state); /* * We have to check for the last task frame at two different locations @@ -277,10 +287,14 @@ bad_address: /* * Don't warn if the unwinder got lost due to an interrupt in entry - * code before the stack was set up: + * code or in the C handler before the first frame pointer got set up: */ if (state->got_irq && in_entry_code(state->ip)) goto the_end; + if (state->regs && + state->regs->sp >= (unsigned long)last_aligned_frame(state) && + state->regs->sp < (unsigned long)task_pt_regs(state->task)) + goto the_end; if (state->regs) { printk_deferred_once(KERN_WARNING -- 2.20.1