[PATCH 3.19 059/177] x86/fpu/xsaves: Fix improper uses of __ex_table

Greg Kroah-Hartman
2015-03-16T15:46:01Z

From: Quentin Casasnovas <quentin.casasnovas@oracle.com>

commit 06c8173eb92bbfc03a0fe8bb64315857d0badd06 upstream.

Commit:

f31a9f7c7169 ("x86/xsaves: Use xsaves/xrstors to save and restore xsave area")

introduced alternative instructions for XSAVES/XRSTORS and commit:

adb9d526e982 ("x86/xsaves: Add xsaves and xrstors support for booting time")

added support for the XSAVES/XRSTORS instructions at boot time.

Unfortunately both failed to properly protect them against faulting:

The 'xstate_fault' macro will use the closest label named '1'
backward and that ends up in the .altinstr_replacement section
rather than in .text. This means that the kernel will never find
in the __ex_table the .text address where this instruction might
fault, leading to serious problems if userspace manages to
trigger the fault.

Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: Jamie Iles <jamie.iles@oracle.com>
[ Improved the changelog, fixed some whitespace noise. ]
Acked-by: Borislav Petkov <bp@alien8.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Allan Xavier <mr.a.xavier@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: adb9d526e982 ("x86/xsaves: Add xsaves and xrstors support for booting time")
Fixes: f31a9f7c7169 ("x86/xsaves: Use xsaves/xrstors to save and restore xsave area")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/include/asm/xsave.h | 28 +++++++++++-----------------
1 file changed, 11 insertions(+), 17 deletions(-)

--- a/arch/x86/include/asm/xsave.h
+++ b/arch/x86/include/asm/xsave.h
@@ -82,18 +82,15 @@ static inline int xsave_state_booting(st
if (boot_cpu_has(X86_FEATURE_XSAVES))
asm volatile("1:"XSAVES"\n\t"
"2:\n\t"
- : : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
+ xstate_fault
+ : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
: "memory");
else
asm volatile("1:"XSAVE"\n\t"
"2:\n\t"
- : : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
+ xstate_fault
+ : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
: "memory");
-
- asm volatile(xstate_fault
- : "0" (0)
- : "memory");
-
return err;
}

@@ -112,18 +109,15 @@ static inline int xrstor_state_booting(s
if (boot_cpu_has(X86_FEATURE_XSAVES))
asm volatile("1:"XRSTORS"\n\t"
"2:\n\t"
- : : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
+ xstate_fault
+ : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
: "memory");
else
asm volatile("1:"XRSTOR"\n\t"
"2:\n\t"
- : : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
+ xstate_fault
+ : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
: "memory");
-
- asm volatile(xstate_fault
- : "0" (0)
- : "memory");
-
return err;
}

@@ -149,9 +143,9 @@ static inline int xsave_state(struct xsa
*/
alternative_input_2(
"1:"XSAVE,
- "1:"XSAVEOPT,
+ XSAVEOPT,
X86_FEATURE_XSAVEOPT,
- "1:"XSAVES,
+ XSAVES,
X86_FEATURE_XSAVES,
[fx] "D" (fx), "a" (lmask), "d" (hmask) :
"memory");
@@ -178,7 +172,7 @@ static inline int xrstor_state(struct xs
*/
alternative_input(
"1: " XRSTOR,
- "1: " XRSTORS,
+ XRSTORS,
X86_FEATURE_XSAVES,
"D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
: "memory");