x86/entry/64: Fix stack return address retrieval in thunk

With CONFIG_FRAME_POINTER enabled, a thunk can pass a bad return address
value to the called function.  '9*8(%rsp)' actually gets the frame
pointer, not the return address.

The only users of the 'put_ret_addr_in_rdi' option are two functions
which trace the enabling and disabling of interrupts, so this bug can
result in bad debug or tracing information with CONFIG_IRQSOFF_TRACER or
CONFIG_PROVE_LOCKING.

Fix this by implementing the suggestion of Linus: explicitly push
the frame pointer all the time and constify the stack offsets that
way. This is both correct and easier to read.

Reported-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
[ Extended the changelog a bit. ]
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alex Thorlton <athorlton@sgi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 058fb73274f9 ("x86/asm/entry: Create stack frames in thunk functions")
Link: http://lkml.kernel.org/r/20160517180606.v5o7wcgdni7443ol@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 5 insertions, 6 deletions

diff --git a/arch/x86/entry/thunk_64.S b/arch/x86/entry/thunk_64.S
index 98df1fa8825c..027aec4a74df 100644
--- a/arch/x86/entry/thunk_64.S
+++ b/arch/x86/entry/thunk_64.S
@@ -8,16 +8,15 @@
 #include <linux/linkage.h>
 #include "calling.h"
 #include <asm/asm.h>
-#include <asm/frame.h>
 
         /* rdi: arg1 ... normal C conventions. rax is saved/restored. */
         .macro THUNK name, func, put_ret_addr_in_rdi=0
         .globl \name
         .type \name, @function
 \name:
-        FRAME_BEGIN
+        pushq %rbp
+        movq %rsp, %rbp
 
-        /* this one pushes 9 elems, the next one would be %rIP */
         pushq %rdi
         pushq %rsi
         pushq %rdx
@@ -29,8 +28,8 @@
         pushq %r11
 
         .if \put_ret_addr_in_rdi
-        /* 9*8(%rsp) is return addr on stack */
-        movq 9*8(%rsp), %rdi
+        /* 8(%rbp) is return addr on stack */
+        movq 8(%rbp), %rdi
         .endif
 
         call \func
@@ -65,7 +64,7 @@ restore:
         popq %rdx
         popq %rsi
         popq %rdi
-        FRAME_END
+        popq %rbp
         ret
         _ASM_NOKPROBE(restore)
 #endif