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Subject[PATCH V6 01/49] x86/entry: Add fence for kernel entry swapgs in paranoid_entry()
Date
From: Lai Jiangshan <laijs@linux.alibaba.com>

Commit 18ec54fdd6d18 ("x86/speculation: Prepare entry code for Spectre
v1 swapgs mitigations") adds FENCE_SWAPGS_{KERNEL|USER}_ENTRY
for conditional swapgs. And in paranoid_entry(), it uses only
FENCE_SWAPGS_KERNEL_ENTRY for both branches. It is because the fence
is required for both cases since the CR3 write is conditinal even PTI
is enabled.

But commit 96b2371413e8f ("x86/entry/64: Switch CR3 before SWAPGS in
paranoid entry") switches the code order and changes the branches.
And it misses the needed FENCE_SWAPGS_KERNEL_ENTRY for user gsbase case.

Add it back by changing the branches so that FENCE_SWAPGS_KERNEL_ENTRY
can cover both branches.

Fixes: Commit 96b2371413e8f ("x86/entry/64: Switch CR3 before SWAPGS in paranoid entry")
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/entry/entry_64.S | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index e38a4cf795d9..8582709576bf 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -897,11 +897,12 @@ SYM_CODE_START_LOCAL(paranoid_entry)
movl $MSR_GS_BASE, %ecx
rdmsr
testl %edx, %edx
- jns .Lparanoid_entry_swapgs
- ret
+ js .Lparanoid_kernel_gsbase

-.Lparanoid_entry_swapgs:
+ /* EBX = 0 -> SWAPGS required on exit */
+ xorl %ebx, %ebx
swapgs
+.Lparanoid_kernel_gsbase:

/*
* The above SAVE_AND_SWITCH_TO_KERNEL_CR3 macro doesn't do an
@@ -909,9 +910,6 @@ SYM_CODE_START_LOCAL(paranoid_entry)
* to prevent GS speculation, regardless of whether PTI is enabled.
*/
FENCE_SWAPGS_KERNEL_ENTRY
-
- /* EBX = 0 -> SWAPGS required on exit */
- xorl %ebx, %ebx
ret
SYM_CODE_END(paranoid_entry)

--
2.19.1.6.gb485710b
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