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From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
	Keith Packard <keithpac@amazon.com>,
	Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
	Linus Walleij <linus.walleij@linaro.org>
Subject: Re: [PATCH v4 4/5] ARM: smp: Store current pointer in TPIDRURO register if available
Date: Mon, 13 Sep 2021 12:22:43 +0100	[thread overview]
Message-ID: <YT80gzXA2mntuaY3@shell.armlinux.org.uk> (raw)
In-Reply-To: <20210913104001.3043132-5-ardb@kernel.org>

On Mon, Sep 13, 2021 at 12:40:00PM +0200, Ard Biesheuvel wrote:
> @@ -767,13 +769,18 @@ ENTRY(__switch_to)
>  	mcr	p15, 0, r6, c3, c0, 0		@ Set domain register
>  #endif
>  	mov	r5, r0
> -	add	r4, r2, #TI_CPU_SAVE
> +	mov	r4, r2
>  	ldr	r0, =thread_notify_head
>  	mov	r1, #THREAD_NOTIFY_SWITCH
>  	bl	atomic_notifier_call_chain
>  #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP)
>  	str	r7, [r8]
>  #endif
> +#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
> +	ldr	ip, [r4, #TI_TASK]
> +	set_current ip
> +#endif
> +	add	r4, r4, #TI_CPU_SAVE
>   THUMB(	mov	ip, r4			   )
>  	mov	r0, r5
>   ARM(	ldmia	r4, {r4 - sl, fp, sp, pc}  )	@ Load all regs saved previously

I would like to keep this as optimal as possible, and the setting of
TPIDRURO to be as close to the stack pointer change too, so I'd
suggest a slightly different approach:

	switch_tls r1, r4, r5, r3, r7
+#if (defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP)) || \
+    defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO)
+	ldr	r9, [r2, #TI_TASK]
+#endif
#if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP)
-	ldr	r7, [r2, #TI_TASK]
	ldr	r8, =__stack_chk_guard
	.if (TSK_STACK_CANARY > IMM12_MASK)
-	add	r7, r7, #TSK_STACK_CANARY & ~IMM12_MASK
-	.endif
+	add	r7, r9, #TSK_STACK_CANARY & ~IMM12_MASK
	ldr	r7, [r7, #TSK_STACK_CANARY & IMM12_MASK]
+	.else
+	ldr	r7, [r9, #TSK_STACK_CANARY & IMM12_MASK]
+	.endif
#endif
...
	mov	r0, r5
+#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
+	set_current r9
+#endif
 ARM(	ldmia	r4, {r4 - sl, fp, sp, pc}  )	@ Load all regs saved previously

It's a slightly more complex change, but one I think we should do.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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  reply	other threads:[~2021-09-13 11:26 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-13 10:39 [PATCH v4 0/5] ARM: support THREAD_INFO_IN_TASK Ard Biesheuvel
2021-09-13 10:39 ` [PATCH v4 1/5] gcc-plugins: arm-ssp: Prepare for THREAD_INFO_IN_TASK support Ard Biesheuvel
2021-09-13 15:40   ` Kees Cook
2021-09-14 22:04   ` Linus Walleij
2021-09-15  6:37     ` Ard Biesheuvel
2021-09-15 16:26       ` Kees Cook
2021-09-13 10:39 ` [PATCH v4 2/5] ARM: smp: Pass task to secondary_start_kernel Ard Biesheuvel
2021-09-13 23:25   ` Linus Walleij
2021-09-13 10:39 ` [PATCH v4 3/5] ARM: smp: Free up the TLS register while running in the kernel Ard Biesheuvel
2021-09-13 10:40 ` [PATCH v4 4/5] ARM: smp: Store current pointer in TPIDRURO register if available Ard Biesheuvel
2021-09-13 11:22   ` Russell King (Oracle) [this message]
2021-09-13 12:52     ` Ard Biesheuvel
2021-09-13 13:52       ` Russell King (Oracle)
2021-09-13 10:40 ` [PATCH v4 5/5] ARM: smp: Enable THREAD_INFO_IN_TASK Ard Biesheuvel
2021-09-13 11:23 ` [PATCH v4 0/5] ARM: support THREAD_INFO_IN_TASK Russell King (Oracle)
2021-09-13 15:40 ` Kees Cook
2021-09-14  9:44 ` Arnd Bergmann
2021-09-14  9:50   ` Ard Biesheuvel
2021-09-14 13:07     ` Arnd Bergmann
2021-09-14 17:10       ` Ard Biesheuvel

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