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authorLai Jiangshan <laijs@linux.alibaba.com>2021-11-26 18:11:22 +0800
committerBorislav Petkov <bp@suse.de>2021-12-03 19:13:53 +0100
commit1367afaa2ee90d1c956dfc224e199fcb3ff3f8cc (patch)
tree19d948b14420f3ff5327c15adfea84543e7bd4d2 /arch
parentc07e45553da1808aa802e9f0ffa8108cfeaf7a17 (diff)
x86/entry: Use the correct fence macro after swapgs in kernel CR3
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
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/entry/entry_64.S15
1 files changed, 8 insertions, 7 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f1a8b5b2af96..f9e1c06a1c32 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -987,11 +987,6 @@ 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
@@ -1014,8 +1009,14 @@ 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 */