Messages in this thread Patch in this message | | | From | Lai Jiangshan <> | Subject | [PATCH V6 01/49] x86/entry: Add fence for kernel entry swapgs in paranoid_entry() | Date | Fri, 26 Nov 2021 18:11:21 +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 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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