linux-kernel - Re: [PATCH v3 3/7] arm: use fixmap for text patching when text is RO

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Date:	Tue, 12 Aug 2014 14:47:37 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Rob Herring <robh@...nel.org>,
	Laura Abbott <lauraa@...eaurora.org>,
	Liu hua <sdu.liu@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Tomasz Figa <t.figa@...sung.com>,
	Jason Wessel <jason.wessel@...driver.com>,
	Will Deacon <will.deacon@....com>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Doug Anderson <dianders@...gle.com>,
	Rabin Vincent <rabin@....in>,
	Nikolay Borisov <Nikolay.Borisov@....com>,
	Mark Salter <msalter@...hat.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 3/7] arm: use fixmap for text patching when text is RO

On Tue, Aug 12, 2014 at 2:39 PM, Stephen Boyd <sboyd@...eaurora.org> wrote:
> On 08/12/14 11:24, Kees Cook wrote:
>> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
>> index 07314af47733..03dd4e39c833 100644
>> --- a/arch/arm/kernel/patch.c
>> +++ b/arch/arm/kernel/patch.c
>> @@ -13,21 +16,69 @@ struct patch {
>>       unsigned int insn;
>>  };
>>
>> -void __kprobes __patch_text(void *addr, unsigned int insn)
>> +static DEFINE_SPINLOCK(patch_lock);
>> +
>> +static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
>> +{
>> +     unsigned int uintaddr = (uintptr_t) addr;
>> +     bool module = !core_kernel_text(uintaddr);
>> +     struct page *page;
>> +
>> +     if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX))
>> +             page = vmalloc_to_page(addr);
>> +     else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA))
>> +             page = virt_to_page(addr);
>> +     else
>> +             return addr;
>> +
>> +     if (flags)
>> +             spin_lock_irqsave(&patch_lock, *flags);
>> +
>> +     set_fixmap(fixmap, page_to_phys(page));
>> +
>> +     return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
>> +}
>> +
>> +static void __kprobes patch_unmap(int fixmap, unsigned long *flags)
>> +{
>> +     clear_fixmap(fixmap);
>> +
>> +     if (flags)
>> +             spin_unlock_irqrestore(&patch_lock, *flags);
>> +}
>
> Has the kbuildbot complained about this one yet?
>
>   CHECK  arch/arm/kernel/patch.c
>   arch/arm/kernel/patch.c:47:39: warning: context imbalance in
> 'patch_unmap' - unexpected unlock
>
> I guess we're going to ignore it.

No, nothing yet from buildbot, let me do a sparse run -- I think we
can just add annotation and we'll be okay.

-Kees

-- 
Kees Cook
Chrome OS Security
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