From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Mon, 9 Oct 2017 20:20:03 -0500
Subject: x86/unwind: Use MSB for frame pointer encoding on 32-bit
Git-commit: 5c99b692cfd62f6915ed7ee7ed3c38d65ba3feab
Patch-mainline: v4.14-rc5
References: bnc#1058115
On x86-32, Tetsuo Handa and Fengguang Wu reported unwinder warnings
like:
WARNING: kernel stack regs at f60bb9c8 in swapper:1 has bad 'bp' value 0ba00000
And also there were some stack dumps with a bunch of unreliable '?'
symbols after an apic_timer_interrupt symbol, meaning the unwinder got
confused when it tried to read the regs.
The cause of those issues is that, with GCC 4.8 (and possibly older),
there are cases where GCC misaligns the stack pointer in a leaf function
for no apparent reason:
c124a388 <acpi_rs_move_data>:
c124a388: 55 push %ebp
c124a389: 89 e5 mov %esp,%ebp
c124a38b: 57 push %edi
c124a38c: 56 push %esi
c124a38d: 89 d6 mov %edx,%esi
c124a38f: 53 push %ebx
c124a390: 31 db xor %ebx,%ebx
c124a392: 83 ec 03 sub $0x3,%esp
...
c124a3e3: 83 c4 03 add $0x3,%esp
c124a3e6: 5b pop %ebx
c124a3e7: 5e pop %esi
c124a3e8: 5f pop %edi
c124a3e9: 5d pop %ebp
c124a3ea: c3 ret
If an interrupt occurs in such a function, the regs on the stack will be
unaligned, which breaks the frame pointer encoding assumption. So on
32-bit, use the MSB instead of the LSB to encode the regs.
This isn't an issue on 64-bit, because interrupts align the stack before
writing to it.
Reported-and-tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-and-tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: LKP <lkp@01.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/279a26996a482ca716605c7dbc7f2db9d8d91e81.1507597785.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
arch/x86/entry/entry_32.S | 4 ++--
arch/x86/kernel/unwind_frame.c | 12 ++++++++++++
2 files changed, 14 insertions(+), 2 deletions(-)
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -176,7 +176,7 @@
/*
* This is a sneaky trick to help the unwinder find pt_regs on the stack. The
* frame pointer is replaced with an encoded pointer to pt_regs. The encoding
- * is just setting the LSB, which makes it an invalid stack address and is also
+ * is just clearing the MSB, which makes it an invalid stack address and is also
* a signal to the unwinder that it's a pt_regs pointer in disguise.
*
* NOTE: This macro must be used *after* SAVE_ALL because it corrupts the
@@ -185,7 +185,7 @@
.macro ENCODE_FRAME_POINTER
#ifdef CONFIG_FRAME_POINTER
mov %esp, %ebp
- orl $0x1, %ebp
+ andl $0x7fffffff, %ebp
#endif
.endm
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -176,6 +176,7 @@ static bool is_last_task_frame(struct un
* This determines if the frame pointer actually contains an encoded pointer to
* pt_regs on the stack. See ENCODE_FRAME_POINTER.
*/
+#ifdef CONFIG_X86_64
static struct pt_regs *decode_frame_pointer(unsigned long *bp)
{
unsigned long regs = (unsigned long)bp;
@@ -185,6 +186,17 @@ static struct pt_regs *decode_frame_poin
return (struct pt_regs *)(regs & ~0x1);
}
+#else
+static struct pt_regs *decode_frame_pointer(unsigned long *bp)
+{
+ unsigned long regs = (unsigned long)bp;
+
+ if (regs & 0x80000000)
+ return NULL;
+
+ return (struct pt_regs *)(regs | 0x80000000);
+}
+#endif
#ifdef CONFIG_X86_32
#define KERNEL_REGS_SIZE (sizeof(struct pt_regs) - 2*sizeof(long))