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authorJosh Poimboeuf <jpoimboe@redhat.com>2016-12-16 10:05:05 -0600
committerThomas Gleixner <tglx@linutronix.de>2016-12-19 11:47:05 +0100
commit8023e0e2a48d45e8d5363081fad9f7ed4402f953 (patch)
tree07a25a758394008d37db6f6a76c8c988c03d0e49 /arch
parent22d3c0d63b1108af0b4ef1cfdad1f6ef0710da30 (diff)
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x86/unwind: Adjust last frame check for aligned function stacks
Somehow, CONFIG_PARAVIRT=n convinces gcc to change the x86_64_start_kernel() prologue from: 0000000000000129 <x86_64_start_kernel>: 129: 55 push %rbp 12a: 48 89 e5 mov %rsp,%rbp to: 0000000000000124 <x86_64_start_kernel>: 124: 4c 8d 54 24 08 lea 0x8(%rsp),%r10 129: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp 12d: 41 ff 72 f8 pushq -0x8(%r10) 131: 55 push %rbp 132: 48 89 e5 mov %rsp,%rbp This is an unusual pattern which aligns rsp (though in this case it's already aligned) and saves the start_cpu() return address again on the stack before storing the frame pointer. The unwinder assumes the last stack frame header is at a certain offset, but the above code breaks that assumption, resulting in the following warning: WARNING: kernel stack frame pointer at ffffffff82e03f40 in swapper:0 has bad value (null) Fix it by checking for the last task stack frame at the aligned offset in addition to the normal unaligned offset. Fixes: acb4608ad186 ("x86/unwind: Create stack frames for saved syscall registers") Reported-by: Borislav Petkov <bp@alien8.de> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Andy Lutomirski <luto@amacapital.net> Link: http://lkml.kernel.org/r/9d7b4eb8cf55a7d6002cb738f25c23e7429c99a0.1481904011.git.jpoimboe@redhat.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/unwind_frame.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index ea7b7f9a3b9e..33aeaae961aa 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -46,7 +46,14 @@ static bool is_last_task_frame(struct unwind_state *state)
unsigned long bp = (unsigned long)state->bp;
unsigned long regs = (unsigned long)task_pt_regs(state->task);
- return bp == regs - FRAME_HEADER_SIZE;
+ /*
+ * We have to check for the last task frame at two different locations
+ * because gcc can occasionally decide to realign the stack pointer and
+ * change the offset of the stack frame by a word in the prologue of a
+ * function called by head/entry code.
+ */
+ return bp == regs - FRAME_HEADER_SIZE ||
+ bp == regs - FRAME_HEADER_SIZE - sizeof(long);
}
/*