| From e3b6d4da55bc8a47d47384b83d435c32eb21e1fc Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Fri, 26 Nov 2021 18:11:22 +0800 |
| Subject: x86/entry: Use the correct fence macro after swapgs in kernel CR3 |
| |
| 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 */ |
| -- |
| 2.33.0 |
| |
