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Subject[PATCH 4/8] x86/segments/64: When load_gs_index fails, clear the base
Date
On AMD CPUs, a failed load_gs_base currently may not clear the FS
base. Fix it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/entry/entry_64.S | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 1693c17dbf81..6344629ae1ce 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -794,6 +794,12 @@ END(native_load_gs_index)
/* running with kernelgs */
bad_gs:
SWAPGS /* switch back to user gs */
+.macro ZAP_GS
+ /* This can't be a string because the preprocessor needs to see it. */
+ movl $__USER_DS, %eax
+ movl %eax, %gs
+.endm
+ ALTERNATIVE "", "ZAP_GS", X86_BUG_NULL_SEG
xorl %eax, %eax
movl %eax, %gs
jmp 2b
--
2.5.5
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