From: Lai Jiangshan laijs@linux.alibaba.com
[ Upstream commit 1367afaa2ee90d1c956dfc224e199fcb3ff3f8cc ]
The commit
c75890700455 ("x86/entry/64: Remove unneeded kernel CR3 switching")
removed a CR3 write in the faulting path of load_gs_index().
But the path's FENCE_SWAPGS_USER_ENTRY has no fence operation if PTI is enabled, see spectre_v1_select_mitigation().
Rather, it depended on the serializing CR3 write of SWITCH_TO_KERNEL_CR3 and since it got removed, add a FENCE_SWAPGS_KERNEL_ENTRY call to make sure speculation is blocked.
[ bp: Massage commit message and comment. ]
Fixes: c75890700455 ("x86/entry/64: Remove unneeded kernel CR3 switching") Signed-off-by: Lai Jiangshan laijs@linux.alibaba.com Signed-off-by: Borislav Petkov bp@suse.de Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20211126101209.8613-3-jiangshanlai@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/entry/entry_64.S | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index f18f3932e971a..a806d68b96990 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1035,11 +1035,6 @@ SYM_CODE_START_LOCAL(error_entry) pushq %r12 ret
-.Lerror_entry_done_lfence: - FENCE_SWAPGS_KERNEL_ENTRY -.Lerror_entry_done: - ret - /* * There are two places in the kernel that can potentially fault with * usergs. Handle them here. B stepping K8s sometimes report a @@ -1062,8 +1057,14 @@ SYM_CODE_START_LOCAL(error_entry) * .Lgs_change's error handler with kernel gsbase. */ SWAPGS - FENCE_SWAPGS_USER_ENTRY - jmp .Lerror_entry_done + + /* + * Issue an LFENCE to prevent GS speculation, regardless of whether it is a + * kernel or user gsbase. + */ +.Lerror_entry_done_lfence: + FENCE_SWAPGS_KERNEL_ENTRY + ret
.Lbstep_iret: /* Fix truncated RIP */