diff options
authorJosh Poimboeuf <jpoimboe@redhat.com>2017-09-28 16:58:26 -0500
committerIngo Molnar <mingo@kernel.org>2017-09-29 13:15:44 +0200
commit520a13c530aeb5f63e011d668c42db1af19ed349 (patch)
parent29b46dfb136cdbeece542b3f01115237e43f2855 (diff)
x86/asm: Fix inline asm call constraints for GCC 4.4
The kernel test bot (run by Xiaolong Ye) reported that the following commit: f5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang") is causing double faults in a kernel compiled with GCC 4.4. Linus subsequently diagnosed the crash pattern and the buggy commit and found that the issue is with this code: register unsigned int __asm_call_sp asm("esp"); #define ASM_CALL_CONSTRAINT "+r" (__asm_call_sp) Even on a 64-bit kernel, it's using ESP instead of RSP. That causes GCC to produce the following bogus code: ffffffff8147461d: 89 e0 mov %esp,%eax ffffffff8147461f: 4c 89 f7 mov %r14,%rdi ffffffff81474622: 4c 89 fe mov %r15,%rsi ffffffff81474625: ba 20 00 00 00 mov $0x20,%edx ffffffff8147462a: 89 c4 mov %eax,%esp ffffffff8147462c: e8 bf 52 05 00 callq ffffffff814c98f0 <copy_user_generic_unrolled> Despite the absurdity of it backing up and restoring the stack pointer for no reason, the bug is actually the fact that it's only backing up and restoring the lower 32 bits of the stack pointer. The upper 32 bits are getting cleared out, corrupting the stack pointer. So change the '__asm_call_sp' register variable to be associated with the actual full-size stack pointer. This also requires changing the __ASM_SEL() macro to be based on the actual compiled arch size, rather than the CONFIG value, because CONFIG_X86_64 compiles some files with '-m32' (e.g., realmode and vdso). Otherwise Clang fails to build the kernel because it complains about the use of a 64-bit register (RSP) in a 32-bit file. Reported-and-Bisected-and-Tested-by: kernel test robot <xiaolong.ye@intel.com> Diagnosed-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Dmitriy Vyukov <dvyukov@google.com> Cc: LKP <lkp@01.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Matthias Kaehlcke <mka@chromium.org> Cc: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: f5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang") Link: http://lkml.kernel.org/r/20170928215826.6sdpmwtkiydiytim@treble Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 files changed, 4 insertions, 2 deletions
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index c1eadbaf1115..30c3c9ac784a 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -11,10 +11,12 @@
# define __ASM_FORM_COMMA(x) " " #x ","
-#ifdef CONFIG_X86_32
+#ifndef __x86_64__
+/* 32 bit */
# define __ASM_SEL(a,b) __ASM_FORM(a)
# define __ASM_SEL_RAW(a,b) __ASM_FORM_RAW(a)
+/* 64 bit */
# define __ASM_SEL(a,b) __ASM_FORM(b)
# define __ASM_SEL_RAW(a,b) __ASM_FORM_RAW(b)
@@ -139,7 +141,7 @@
* gets set up by the containing function. If you forget to do this, objtool
* may print a "call without frame pointer save/setup" warning.
-register unsigned int __asm_call_sp asm("esp");
+register unsigned long __asm_call_sp asm(_ASM_SP);
#define ASM_CALL_CONSTRAINT "+r" (__asm_call_sp)