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Message-ID: <alpine.LFD.2.20.1708141158070.17016@knanqh.ubzr>
Date: Mon, 14 Aug 2017 12:02:42 -0400 (EDT)
From: Nicolas Pitre <nicolas.pitre@...aro.org>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
cc: kernel-hardening@...ts.openwall.com, 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 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.
> /* This ldmia relies on the memory layout of the mpidr_hash struct */
> ldmia r0, {r1, r6-r8} @ r1 = mpidr mask (r6,r7,r8) = l[0,1,2] shifts
> @@ -100,13 +99,13 @@ ENDPROC(cpu_suspend_abort)
> .align 5
> .pushsection .idmap.text,"ax"
> ENTRY(cpu_resume_mmu)
> - ldr r3, =cpu_resume_after_mmu
> instr_sync
> mcr p15, 0, r0, c1, c0, 0 @ turn on MMU, I-cache, etc
> mrc p15, 0, r0, c0, c0, 0 @ read id reg
> instr_sync
> mov r0, r0
> mov r0, r0
> + ldr r3, =cpu_resume_after_mmu
> ret r3 @ jump to virtual address
> ENDPROC(cpu_resume_mmu)
> .popsection
> --
> 2.11.0
>
>
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