x86/fpu/xsaves: Fix improper uses of __ex_table

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: <stable@vger.kernel.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>

1 files changed, 11 insertions, 17 deletions

diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h
index 5fa9770035dc..c9a6d68b8d62 100644
--- a/arch/x86/include/asm/xsave.h
+++ b/arch/x86/include/asm/xsave.h
@@ -82,18 +82,15 @@ static inline int xsave_state_booting(struct xsave_struct *fx, u64 mask)
         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(struct xsave_struct *fx, u64 mask)
         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 xsave_struct *fx, u64 mask)
          */
         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 xsave_struct *fx, u64 mask)
          */
         alternative_input(
                 "1: " XRSTOR,
-                "1: " XRSTORS,
+                XRSTORS,
                 X86_FEATURE_XSAVES,
                 "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
                 : "memory");