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From: Nicolas Pitre <nicolas.pitre@linaro.org>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Russell King <linux@armlinux.org.uk>,
	Kees Cook <keescook@chromium.org>,
	Thomas Garnier <thgarnie@google.com>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Tony Lindgren <tony@atomide.com>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	Dave Martin <dave.martin@arm.com>
Subject: [kernel-hardening] Re: [PATCH 20/30] ARM: kernel: use PC relative symbol references in suspend/resume code
Date: Mon, 14 Aug 2017 14:37:51 -0400 (EDT)	[thread overview]
Message-ID: <alpine.LFD.2.20.1708141434240.17016@knanqh.ubzr> (raw)
In-Reply-To: <CAKv+Gu-k4vUHDz92dsy-d15aBh61-pcGDi3GbX9pmBCbY21SsQ@mail.gmail.com>

On Mon, 14 Aug 2017, Ard Biesheuvel wrote:

> On 14 August 2017 at 17:02, Nicolas Pitre <nicolas.pitre@linaro.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@armlinux.org.uk>
> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.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
> 

Yeah... I see no way around it.

And if you make this particular case into a commit of its own, then the 
commit log may carry the above reasoning.


Nicolas

  reply	other threads:[~2017-08-14 18:37 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-14 12:53 [kernel-hardening] [PATCH 00/30] implement KASLR for ARM Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 01/30] asm-generic: add .data.rel.ro sections to __ro_after_init Ard Biesheuvel
2017-08-14 14:26   ` [kernel-hardening] " Arnd Bergmann
2017-08-14 12:53 ` [kernel-hardening] [PATCH 02/30] ARM: assembler: introduce adr_l, ldr_l and str_l macros Ard Biesheuvel
2017-08-14 15:29   ` [kernel-hardening] " Dave Martin
2017-08-14 15:38     ` Ard Biesheuvel
2017-08-14 15:50       ` Dave Martin
2017-08-14 16:18         ` Nicolas Pitre
2017-08-14 16:22           ` Ard Biesheuvel
2017-08-14 16:33             ` Nicolas Pitre
2017-08-14 16:42             ` Russell King - ARM Linux
2017-08-14 16:56               ` Ard Biesheuvel
2017-08-14 15:32   ` Dave Martin
2017-08-14 15:40     ` Ard Biesheuvel
2017-08-14 15:53       ` Dave Martin
2017-08-14 12:53 ` [kernel-hardening] [PATCH 03/30] ARM: head-common.S: use PC-relative insn sequence for __proc_info Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 04/30] ARM: head-common.S: use PC-relative insn sequence for idmap creation Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 05/30] ARM: head.S: use PC-relative insn sequence for secondary_data Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 06/30] ARM: kernel: use relative references for UP/SMP alternatives Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 07/30] ARM: head: use PC-relative insn sequence for __smp_alt Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 08/30] ARM: sleep.S: use PC-relative insn sequence for sleep_save_sp/mpidr_hash Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 09/30] ARM: head.S: use PC-relative insn sequences for __fixup_pv_table Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 10/30] ARM: head.S: use PC relative insn sequence to calculate PHYS_OFFSET Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 11/30] ARM: kvm: replace open coded VA->PA calculations with adr_l call Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 12/30] arm-soc: exynos: replace open coded VA->PA conversions Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 13/30] arm-soc: mvebu: replace open coded VA->PA conversion Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 14/30] arm-soc: various: replace open coded VA->PA calculation of pen_release Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 15/30] ARM: kernel: switch to relative exception tables Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 16/30] ARM: kernel: use relative phys-to-virt patch tables Ard Biesheuvel
2017-08-14 12:53 ` [kernel-hardening] [PATCH 17/30] arm-soc: tegra: make sleep asm code runtime relocatable Ard Biesheuvel
2017-08-14 14:42   ` [kernel-hardening] " Dave Martin
2017-08-14 14:49     ` Ard Biesheuvel
2017-08-14 15:29       ` Dave Martin
2017-08-14 12:53 ` [kernel-hardening] [PATCH 18/30] ARM: kernel: make vmlinux buildable as a PIE executable Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 19/30] ARM: kernel: use PC-relative symbol references in MMU switch code Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 20/30] ARM: kernel: use PC relative symbol references in suspend/resume code Ard Biesheuvel
2017-08-14 16:02   ` [kernel-hardening] " Nicolas Pitre
2017-08-14 18:14     ` Ard Biesheuvel
2017-08-14 18:37       ` Nicolas Pitre [this message]
2017-08-14 12:54 ` [kernel-hardening] [PATCH 21/30] ARM: mm: export default vmalloc base address Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 22/30] ARM: kernel: refer to swapper_pg_dir via its symbol Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 23/30] ARM: kernel: implement randomization of the kernel load address Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 24/30] ARM: decompressor: explicitly map decompressor binary cacheable Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 25/30] ARM: compressed: factor out zImage header and make it extensible Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 26/30] ARM: decompressor: add KASLR support Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 27/30] efi/libstub: add 'max' parameter to efi_random_alloc() Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 28/30] efi/libstub: check for vmalloc= command line argument Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 29/30] efi/libstub: arm: reserve bootloader supplied initrd in memory map Ard Biesheuvel
2017-08-18 11:48   ` [kernel-hardening] " Ard Biesheuvel
2017-08-21 10:37   ` Mark Rutland
2017-08-21 10:39     ` Ard Biesheuvel
2017-08-14 12:54 ` [kernel-hardening] [PATCH 30/30] efi/libstub: arm: implement KASLR Ard Biesheuvel
2017-08-14 15:30 ` [kernel-hardening] Re: [PATCH 00/30] implement KASLR for ARM Arnd Bergmann
2017-08-14 15:49   ` Ard Biesheuvel
2017-08-14 16:03     ` Arnd Bergmann
2017-08-14 16:28       ` Nicolas Pitre
2017-08-14 17:28         ` Ard Biesheuvel
2017-08-14 18:01           ` Nicolas Pitre
2017-08-14 18:08             ` Ard Biesheuvel
2017-08-14 16:16     ` Nicolas Pitre

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