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Peter Anvin" Subject: [PATCH V3 16/49] x86/traps: Add fence_swapgs_{user,kernel}_entry() Date: Thu, 14 Oct 2021 11:33:39 +0800 Message-Id: <20211014033414.16321-11-jiangshanlai@gmail.com> X-Mailer: git-send-email 2.19.1.6.gb485710b In-Reply-To: <20211014031413.14471-1-jiangshanlai@gmail.com> References: <20211014031413.14471-1-jiangshanlai@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Lai Jiangshan fence_swapgs_{user,kernel}_entry() in entry64.c are the same as the ASM macro FENCE_SWAPGS_{USER,KERNEL}_ENTRY. fence_swapgs_user_entry is used in the user entry swapgs code path, to prevent a speculative swapgs when coming from kernel space. fence_swapgs_kernel_entry is used in the kernel entry code path, to prevent the swapgs from getting speculatively skipped when coming from user space. Cc: Josh Poimboeuf Signed-off-by: Lai Jiangshan --- arch/x86/entry/entry64.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/arch/x86/entry/entry64.c b/arch/x86/entry/entry64.c index 9a5c535b1ddf..bdc9540f25d3 100644 --- a/arch/x86/entry/entry64.c +++ b/arch/x86/entry/entry64.c @@ -38,3 +38,24 @@ static __always_inline void switch_to_kernel_cr3(void) #else static __always_inline void switch_to_kernel_cr3(void) {} #endif + +/* + * Mitigate Spectre v1 for conditional swapgs code paths. + * + * fence_swapgs_user_entry is used in the user entry swapgs code path, to + * prevent a speculative swapgs when coming from kernel space. It must be + * used with switch_to_kernel_cr3() in the same path. + * + * fence_swapgs_kernel_entry is used in the kernel entry code path without + * CR3 write or with conditinal CR3 write only, to prevent the swapgs from + * getting speculatively skipped when coming from user space. + */ +static __always_inline void fence_swapgs_user_entry(void) +{ + alternative("", "lfence", X86_FEATURE_FENCE_SWAPGS_USER); +} + +static __always_inline void fence_swapgs_kernel_entry(void) +{ + alternative("", "lfence", X86_FEATURE_FENCE_SWAPGS_KERNEL); +} -- 2.19.1.6.gb485710b