From 1367afaa2ee90d1c956dfc224e199fcb3ff3f8cc Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Fri, 26 Nov 2021 18:11:22 +0800 Subject: 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 Signed-off-by: Borislav Petkov Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20211126101209.8613-3-jiangshanlai@gmail.com --- arch/x86/entry/entry_64.S | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) (limited to 'arch/x86') 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 */ -- cgit v1.2.3