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From: Peter Zijlstra <peterz@infradead.org>
To: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: linux-kernel@vger.kernel.org,
	Lai Jiangshan <laijs@linux.alibaba.com>,
	Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 09/24] x86/traps: Add fence_swapgs_{user,kernel}_entry()
Date: Thu, 2 Sep 2021 11:25:29 +0200	[thread overview]
Message-ID: <YTCYiUIGeluu8Bov@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210831175025.27570-10-jiangshanlai@gmail.com>

On Wed, Sep 01, 2021 at 01:50:10AM +0800, Lai Jiangshan wrote:

> +/*
> + * 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.
> + *
> + * fence_swapgs_kernel_entry is used in the kernel entry non-swapgs code path,
> + * 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);
> +}

I think slightly larger primitives might make more sense; that is
include the swapgs in these function and drop the fence_ prefix.

Something a bit like...

--- a/arch/x86/entry/traps.c
+++ b/arch/x86/entry/traps.c
@@ -853,20 +853,22 @@ static __always_inline void ist_restore_
 /*
  * 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.
+ * 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 non-swapgs code path,
- * to prevent the swapgs from getting speculatively skipped when coming from
- * user space.
+ * swapgs_kernel_entry is used in the kernel entry non-swapgs code path, to
+ * prevent the swapgs from getting speculatively skipped when coming from user
+ * space.
  */
-static __always_inline void fence_swapgs_user_entry(void)
+static __always_inline void swapgs_user_entry(void)
 {
+	native_swapgs();
 	alternative("", "lfence", X86_FEATURE_FENCE_SWAPGS_USER);
 }
 
-static __always_inline void fence_swapgs_kernel_entry(void)
+static __always_inline void swapgs_kernel_entry(void)
 {
+	native_swapgs();
 	alternative("", "lfence", X86_FEATURE_FENCE_SWAPGS_KERNEL);
 }
 
@@ -896,8 +898,7 @@ struct pt_regs *do_error_entry(struct pt
 		 * We entered from user mode.
 		 * Switch to kernel gsbase and CR3.
 		 */
-		native_swapgs();
-		fence_swapgs_user_entry();
+		swapgs_user_entry();
 		switch_to_kernel_cr3();
 
 		/* Put pt_regs onto the task stack. */
@@ -917,8 +918,7 @@ struct pt_regs *do_error_entry(struct pt
 		 * We came from an IRET to user mode, so we have user
 		 * gsbase and CR3.  Switch to kernel gsbase and CR3:
 		 */
-		native_swapgs();
-		fence_swapgs_user_entry();
+		swapgs_user_entry();
 		switch_to_kernel_cr3();
 
 		/*
@@ -936,8 +936,7 @@ struct pt_regs *do_error_entry(struct pt
 	 * handler with kernel gsbase.
 	 */
 	if (eregs->ip == (unsigned long)asm_load_gs_index_gs_change) {
-		native_swapgs();
-		fence_swapgs_user_entry();
+		swapgs_user_entry();
 	} else {
 		fence_swapgs_kernel_entry();
 	}
@@ -1017,14 +1016,12 @@ static __always_inline unsigned long ist
 	if ((long)gsbase < 0)
 		return 1;
 
-	native_swapgs();
-
 	/*
 	 * The above ist_switch_to_kernel_cr3() doesn't do an unconditional
 	 * CR3 write, even in the PTI case.  So do an lfence to prevent GS
 	 * speculation, regardless of whether PTI is enabled.
 	 */
-	fence_swapgs_kernel_entry();
+	swapgs_kernel_entry();
 
 	/* SWAPGS required on exit */
 	return 0;
@@ -1089,7 +1086,7 @@ void paranoid_exit(struct ist_regs *ist)
 	}
 
 	if (!ist->gsbase)
-		native_swapgs();
+		swapgs_user_entry();
 }
 #endif
 

  reply	other threads:[~2021-09-02  9:26 UTC|newest]

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-31 17:50 [PATCH 00/24] x86/entry/64: Convert a bunch of ASM entry code into C code Lai Jiangshan
2021-08-31 17:50 ` [PATCH 01/24] x86/traps: Remove stack-protector from traps.c Lai Jiangshan
2021-08-31 17:50 ` [PATCH 02/24] x86/traps: Move arch/x86/kernel/traps.c to arch/x86/entry/ Lai Jiangshan
2021-09-02  8:09   ` Joerg Roedel
2021-09-02  9:21     ` Lai Jiangshan
2021-09-02 10:50       ` Peter Zijlstra
2021-09-02 11:54         ` Lai Jiangshan
2021-09-02 12:05           ` Peter Zijlstra
2021-09-02 13:34             ` Peter Zijlstra
2021-09-02 17:05               ` Nick Desaulniers
2021-09-02 17:19                 ` Miguel Ojeda
2021-09-02 17:23                   ` Nick Desaulniers
2021-09-03  7:36                 ` Martin Liška
2021-09-07 21:12                   ` Nick Desaulniers
2021-09-08  7:33                     ` Martin Liška
2021-08-31 17:50 ` [PATCH 03/24] x86/traps: Move declaration of native_irq_return_iret up Lai Jiangshan
2021-08-31 17:50 ` [PATCH 04/24] x86/entry: Expose the address of .Lgs_change to traps.c Lai Jiangshan
2021-09-02  9:14   ` Peter Zijlstra
2021-09-02  9:20     ` Lai Jiangshan
2021-08-31 17:50 ` [PATCH 05/24] x86/entry: Introduce __entry_text for entry code written in C Lai Jiangshan
2021-08-31 19:34   ` Peter Zijlstra
2021-09-01  0:23     ` Lai Jiangshan
2021-08-31 17:50 ` [PATCH 06/24] x86/entry: Move PTI_USER_* to arch/x86/include/asm/processor-flags.h Lai Jiangshan
2021-08-31 17:50 ` [PATCH 07/24] x86: Mark __native_read_cr3() & native_write_cr3() as __always_inline Lai Jiangshan
2021-08-31 17:50 ` [PATCH 08/24] x86/traps: Add C verion of SWITCH_TO_KERNEL_CR3 as switch_to_kernel_cr3() Lai Jiangshan
2021-08-31 17:50 ` [PATCH 09/24] x86/traps: Add fence_swapgs_{user,kernel}_entry() Lai Jiangshan
2021-09-02  9:25   ` Peter Zijlstra [this message]
2021-08-31 17:50 ` [PATCH 10/24] x86/traps: Move pt_regs only in fixup_bad_iret() Lai Jiangshan
2021-08-31 17:50 ` [PATCH 11/24] x86/entry: Replace the most of asm code of error_entry to C code Lai Jiangshan
2021-09-02 10:16   ` Peter Zijlstra
2021-09-02 12:08     ` Lai Jiangshan
2021-08-31 17:50 ` [PATCH 12/24] x86/traps: Reconstruct pt_regs on task stack directly in fixup_bad_iret() Lai Jiangshan
2021-08-31 17:50 ` [PATCH 13/24] x86/traps: Mark sync_regs() and fixup_bad_iret() as static __always_inline Lai Jiangshan
2021-08-31 17:50 ` [PATCH 14/24] x86/entry: Make paranoid_exit() callable Lai Jiangshan
2021-08-31 17:50 ` [PATCH 15/24] x86/entry: Call paranoid_exit() in asm_exc_nmi() Lai Jiangshan
2021-08-31 17:50 ` [PATCH 16/24] x86/entry: Use skip_rdi instead of save_ret for PUSH_AND_CLEAR_REGS Lai Jiangshan
2021-08-31 17:50 ` [PATCH 17/24] x86/entry: Introduce struct ist_regs Lai Jiangshan
2021-09-10  0:18   ` Lai Jiangshan
2021-09-10  0:36     ` Lai Jiangshan
2021-09-10  4:31     ` H. Peter Anvin
2021-09-10  7:13       ` Lai Jiangshan
2021-09-10  7:14         ` H. Peter Anvin
2021-09-10  4:50     ` H. Peter Anvin
2021-09-10  4:51       ` H. Peter Anvin
2021-08-31 17:50 ` [PATCH 18/24] x86/entry: Add the C version ist_switch_to_kernel_cr3() Lai Jiangshan
2021-08-31 17:50 ` [PATCH 19/24] x86/entry: Add the C version ist_restore_cr3() Lai Jiangshan
2021-08-31 17:50 ` [PATCH 20/24] x86/entry: Add the C version get_percpu_base() Lai Jiangshan
2021-08-31 17:50 ` [PATCH 21/24] x86/entry: Add the C version ist_switch_to_kernel_gsbase() Lai Jiangshan
2021-08-31 17:50 ` [PATCH 22/24] x86/entry: Implement and use do_paranoid_entry() and paranoid_exit() Lai Jiangshan
2021-09-02 10:33   ` Peter Zijlstra
2021-09-02 10:42     ` Lai Jiangshan
2021-09-02 12:02       ` Peter Zijlstra
2021-09-02 11:58     ` Lai Jiangshan
2021-09-02 12:29       ` Joerg Roedel
2021-08-31 17:50 ` [PATCH 23/24] x86/entry: Remove the unused ASM macros Lai Jiangshan
2021-08-31 17:50 ` [PATCH 24/24] x86/syscall/64: Move the checking for sysret to C code Lai Jiangshan
2021-09-10  7:20   ` Nikolay Borisov
2021-09-10  7:30     ` Lai Jiangshan
2021-08-31 20:44 ` [PATCH 00/24] x86/entry/64: Convert a bunch of ASM entry code into " Peter Zijlstra
2021-09-02  6:28   ` Lai Jiangshan
2021-09-02  7:44     ` Peter Zijlstra
2021-09-02 10:50 ` [PATCH 25/24] x86/traps: Rewrite native_load_gs_index in " Lai Jiangshan
2021-09-08  1:38   ` H. Peter Anvin
2021-09-08  4:42     ` H. Peter Anvin
2021-09-08  5:00       ` H. Peter Anvin
2021-09-08  7:12         ` Lai Jiangshan
2021-09-09 23:16           ` H. Peter Anvin
2021-09-13 20:01   ` Andy Lutomirski
2021-09-14  2:04     ` Lai Jiangshan
2021-09-14  8:14       ` Peter Zijlstra
2021-09-14  8:17         ` Borislav Petkov
2021-09-14  8:40         ` Lai Jiangshan

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