From: Lai Jiangshan laijs@linux.alibaba.com
[ Upstream commit c07e45553da1808aa802e9f0ffa8108cfeaf7a17 ]
Commit
18ec54fdd6d18 ("x86/speculation: Prepare entry code for Spectre v1 swapgs mitigations")
added FENCE_SWAPGS_{KERNEL|USER}_ENTRY for conditional SWAPGS. In paranoid_entry(), it uses only FENCE_SWAPGS_KERNEL_ENTRY for both branches. This is because the fence is required for both cases since the CR3 write is conditional even when PTI is enabled.
But
96b2371413e8f ("x86/entry/64: Switch CR3 before SWAPGS in paranoid entry")
changed the order of SWAPGS and the CR3 write. And it missed the needed FENCE_SWAPGS_KERNEL_ENTRY for the user gsbase case.
Add it back by changing the branches so that FENCE_SWAPGS_KERNEL_ENTRY can cover both branches.
[ bp: Massage, fix typos, remove obsolete comment while at it. ]
Fixes: 96b2371413e8f ("x86/entry/64: Switch CR3 before SWAPGS in paranoid entry") Signed-off-by: Lai Jiangshan laijs@linux.alibaba.com Signed-off-by: Borislav Petkov bp@suse.de Link: https://lkml.kernel.org/r/20211126101209.8613-2-jiangshanlai@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/entry/entry_64.S | 16 +++++----------- 1 file changed, 5 insertions(+), 11 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 166554a109aeb..a24ce5905ab82 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -936,6 +936,7 @@ SYM_CODE_START_LOCAL(paranoid_entry) .Lparanoid_entry_checkgs: /* EBX = 1 -> kernel GSBASE active, no restore required */ movl $1, %ebx + /* * The kernel-enforced convention is a negative GSBASE indicates * a kernel value. No SWAPGS needed on entry and exit. @@ -943,21 +944,14 @@ 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 - * 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 SYM_CODE_END(paranoid_entry)