From e335bb51cc15e80ac180701a0d335ef1c050828e Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Mon, 17 Apr 2017 08:44:00 -0500 Subject: [PATCH] x86/unwind: Ensure stack pointer is aligned With frame pointers disabled, on some older versions of GCC (like 4.8.3), it's possible for the stack pointer to get aligned at a half-word boundary: 00000000000004d0 : 4d0: 41 57 push %r15 4d2: 41 56 push %r14 4d4: 41 55 push %r13 4d6: 41 54 push %r12 4d8: 55 push %rbp 4d9: 53 push %rbx 4da: 48 83 ec 24 sub $0x24,%rsp In such a case, the unwinder ends up reading the entire stack at the wrong alignment. Then the last read goes past the end of the stack, hitting the stack guard page: BUG: stack guard page was hit at ffffc900217c4000 (stack is ffffc900217c0000..ffffc900217c3fff) kernel stack overflow (page fault): 0000 [#1] SMP ... Fix it by ensuring the stack pointer is properly aligned before unwinding. Reported-by: Jirka Hladky Signed-off-by: Josh Poimboeuf Acked-by: Thomas Gleixner Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Fixes: 7c7900f89770 ("x86/unwind: Add new unwind interface and implementations") Link: http://lkml.kernel.org/r/cff33847cc9b02fa548625aa23268ac574460d8d.1492436590.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/dumpstack.c | 2 +- arch/x86/kernel/unwind_guess.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index 924f45ea4382..dbce3cca94cb 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -77,7 +77,7 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs, * - softirq stack * - hardirq stack */ - for (regs = NULL; stack; stack = stack_info.next_sp) { + for (regs = NULL; stack; stack = PTR_ALIGN(stack_info.next_sp, sizeof(long))) { const char *stack_name; /* diff --git a/arch/x86/kernel/unwind_guess.c b/arch/x86/kernel/unwind_guess.c index 22881ddcbb9f..039f36738e49 100644 --- a/arch/x86/kernel/unwind_guess.c +++ b/arch/x86/kernel/unwind_guess.c @@ -34,7 +34,7 @@ bool unwind_next_frame(struct unwind_state *state) return true; } - state->sp = info->next_sp; + state->sp = PTR_ALIGN(info->next_sp, sizeof(long)); } while (!get_stack_info(state->sp, state->task, info, &state->stack_mask)); @@ -49,7 +49,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, memset(state, 0, sizeof(*state)); state->task = task; - state->sp = first_frame; + state->sp = PTR_ALIGN(first_frame, sizeof(long)); get_stack_info(first_frame, state->task, &state->stack_info, &state->stack_mask); -- 2.20.1