Messages in this thread Patch in this message | | | From | Lai Jiangshan <> | Subject | [PATCH V5 01/50] x86/entry: Add fence for kernel entry swapgs in paranoid_entry() | Date | Wed, 10 Nov 2021 19:56:47 +0800 |
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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 moving FENCE_SWAPGS_KERNEL_ENTRY up to 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 | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index e38a4cf795d9..14ffe12807ba 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -888,6 +888,13 @@ SYM_CODE_START_LOCAL(paranoid_entry) ret .Lparanoid_entry_checkgs: + /* + * The above SAVE_AND_SWITCH_TO_KERNEL_CR3 macro doesn't do an + * unconditional CR3 write, even in the PTI case. So do an lfence + * to prevent GS speculation, regardless of whether PTI is enabled. + */ + FENCE_SWAPGS_KERNEL_ENTRY + /* EBX = 1 -> kernel GSBASE active, no restore required */ movl $1, %ebx /* @@ -903,13 +910,6 @@ SYM_CODE_START_LOCAL(paranoid_entry) .Lparanoid_entry_swapgs: swapgs - /* - * The above SAVE_AND_SWITCH_TO_KERNEL_CR3 macro doesn't do an - * unconditional CR3 write, even in the PTI case. So do an lfence - * to prevent GS speculation, regardless of whether PTI is enabled. - */ - FENCE_SWAPGS_KERNEL_ENTRY - /* EBX = 0 -> SWAPGS required on exit */ xorl %ebx, %ebx ret -- 2.19.1.6.gb485710b
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