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Date: Mon, 14 Aug 2017 19:14:40 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Nicolas Pitre <nicolas.pitre@...aro.org>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, Arnd Bergmann <arnd@...db.de>,
Russell King <linux@...linux.org.uk>, Kees Cook <keescook@...omium.org>,
Thomas Garnier <thgarnie@...gle.com>, Marc Zyngier <marc.zyngier@....com>,
Mark Rutland <mark.rutland@....com>, Tony Lindgren <tony@...mide.com>,
Matt Fleming <matt@...eblueprint.co.uk>, Dave Martin <dave.martin@....com>
Subject: Re: [PATCH 20/30] ARM: kernel: use PC relative symbol references in
suspend/resume code
On 14 August 2017 at 17:02, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> On Mon, 14 Aug 2017, Ard Biesheuvel wrote:
>
>> Replace some unnecessary absolute references with relative ones. Also,
>> to prepare for runtime relocation, which occurs with the caches on,
>> defer taking the absolute address of cpu_resume_after_mmu() until after
>> the MMU is enabled.
>>
>> Cc: Russell King <linux@...linux.org.uk>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> ---
>> arch/arm/kernel/sleep.S | 11 +++++------
>> 1 file changed, 5 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm/kernel/sleep.S b/arch/arm/kernel/sleep.S
>> index 3026b119d3ff..9efd1c7d3552 100644
>> --- a/arch/arm/kernel/sleep.S
>> +++ b/arch/arm/kernel/sleep.S
>> @@ -60,18 +60,17 @@
>> ENTRY(__cpu_suspend)
>> stmfd sp!, {r4 - r11, lr}
>> #ifdef MULTI_CPU
>> - ldr r10, =processor
>> - ldr r4, [r10, #CPU_SLEEP_SIZE] @ size of CPU sleep state
>> + ldr_l r4, processor + CPU_SLEEP_SIZE @ size of CPU sleep state
>> #else
>> - ldr r4, =cpu_suspend_size
>> + adr_l r4, cpu_suspend_size
>> #endif
>> mov r5, sp @ current virtual SP
>> add r4, r4, #12 @ Space for pgd, virt sp, phys resume fn
>> sub sp, sp, r4 @ allocate CPU state on stack
>> - ldr r3, =sleep_save_sp
>> + adr_l r3, sleep_save_sp
>> stmfd sp!, {r0, r1} @ save suspend func arg and pointer
>> ldr r3, [r3, #SLEEP_SAVE_SP_VIRT]
>> - ALT_SMP(ldr r0, =mpidr_hash)
>> + ALT_SMP(adr_l r0, mpidr_hash)
>> ALT_UP_B(1f)
>
> The above is dangerous. adr_l expands to more than one instruction which
> is not what ALT_SMP() was designed for. Here it might happen to work
> anyway because it is combined with ALT_UP_B() but with ALT_UP() it
> wouldn't. This is a mistake waiting to happen.
>
OK. I will use the opencoded sequence instead in this case. I.e.,
- ALT_SMP(ldr r0, =mpidr_hash)
+0: ALT_SMP(adr r0, 2f)
ALT_UP_B(1f)
+ ldr r1, [r0]
+ add r0, r0, r1
and
ENDPROC(__cpu_suspend)
+ .align 2
+2: .long mpidr_hash - .
.ltorg
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