diff options
Diffstat (limited to 'common/recipes-kernel/linux/linux-yocto-4.9.21/0022-x86-nospec-Simplify-alternative_msr_write.patch')
| -rw-r--r-- | common/recipes-kernel/linux/linux-yocto-4.9.21/0022-x86-nospec-Simplify-alternative_msr_write.patch | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/common/recipes-kernel/linux/linux-yocto-4.9.21/0022-x86-nospec-Simplify-alternative_msr_write.patch b/common/recipes-kernel/linux/linux-yocto-4.9.21/0022-x86-nospec-Simplify-alternative_msr_write.patch new file mode 100644 index 00000000..aef6dcc5 --- /dev/null +++ b/common/recipes-kernel/linux/linux-yocto-4.9.21/0022-x86-nospec-Simplify-alternative_msr_write.patch @@ -0,0 +1,71 @@ +From 0ba8203bd88d5640bd6b062b09d3514d5787161d Mon Sep 17 00:00:00 2001 +From: Linus Torvalds <torvalds@linux-foundation.org> +Date: Tue, 1 May 2018 15:55:51 +0200 +Subject: [PATCH 22/93] x86/nospec: Simplify alternative_msr_write() + +commit 1aa7a5735a41418d8e01fa7c9565eb2657e2ea3f upstream + +The macro is not type safe and I did look for why that "g" constraint for +the asm doesn't work: it's because the asm is more fundamentally wrong. + +It does + + movl %[val], %%eax + +but "val" isn't a 32-bit value, so then gcc will pass it in a register, +and generate code like + + movl %rsi, %eax + +and gas will complain about a nonsensical 'mov' instruction (it's moving a +64-bit register to a 32-bit one). + +Passing it through memory will just hide the real bug - gcc still thinks +the memory location is 64-bit, but the "movl" will only load the first 32 +bits and it all happens to work because x86 is little-endian. + +Convert it to a type safe inline function with a little trick which hands +the feature into the ALTERNATIVE macro. + +Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> +Signed-off-by: Thomas Gleixner <tglx@linutronix.de> +Reviewed-by: Ingo Molnar <mingo@kernel.org> +Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> +Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> +--- + arch/x86/include/asm/nospec-branch.h | 19 ++++++++++--------- + 1 file changed, 10 insertions(+), 9 deletions(-) + +diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h +index f928ad9..870acfc 100644 +--- a/arch/x86/include/asm/nospec-branch.h ++++ b/arch/x86/include/asm/nospec-branch.h +@@ -241,15 +241,16 @@ static inline void vmexit_fill_RSB(void) + #endif + } + +-#define alternative_msr_write(_msr, _val, _feature) \ +- asm volatile(ALTERNATIVE("", \ +- "movl %[msr], %%ecx\n\t" \ +- "movl %[val], %%eax\n\t" \ +- "movl $0, %%edx\n\t" \ +- "wrmsr", \ +- _feature) \ +- : : [msr] "i" (_msr), [val] "i" (_val) \ +- : "eax", "ecx", "edx", "memory") ++static __always_inline ++void alternative_msr_write(unsigned int msr, u64 val, unsigned int feature) ++{ ++ asm volatile(ALTERNATIVE("", "wrmsr", %c[feature]) ++ : : "c" (msr), ++ "a" (val), ++ "d" (val >> 32), ++ [feature] "i" (feature) ++ : "memory"); ++} + + static inline void indirect_branch_prediction_barrier(void) + { +-- +2.7.4 + |