linux-kernel - Re: [PATCH v12 06/10] arm64: Treat all entry code as non-kprobe-able

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Message-ID: <57471589.9030301@linaro.org>
Date:	Thu, 26 May 2016 11:26:01 -0400
From:	David Long <dave.long@...aro.org>
To:	James Morse <james.morse@....com>,
	Pratyush Anand <panand@...hat.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
	William Cohen <wcohen@...hat.com>,
	Steve Capper <steve.capper@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Marc Zyngier <marc.zyngier@....com>,
	Dave P Martin <Dave.Martin@....com>,
	Mark Rutland <mark.rutland@....com>,
	Robin Murphy <Robin.Murphy@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Jens Wiklander <jens.wiklander@...aro.org>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Alex Bennée <alex.bennee@...aro.org>,
	Yang Shi <yang.shi@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"Suzuki K. Poulose" <suzuki.poulose@....com>,
	Kees Cook <keescook@...omium.org>,
	Zi Shen Lim <zlim.lnx@...il.com>,
	John Blackwood <john.blackwood@...r.com>,
	Feng Kan <fkan@....com>,
	Balamurugan Shanmugam <bshanmugam@....com>,
	Vladimir Murzin <Vladimir.Murzin@....com>,
	Mark Salyzyn <salyzyn@...roid.com>,
	Petr Mladek <pmladek@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v12 06/10] arm64: Treat all entry code as non-kprobe-able

On 05/12/2016 10:49 AM, James Morse wrote:
> Hi David, Pratyush
>
> On 27/04/16 19:53, David Long wrote:
>> From: Pratyush Anand <panand@...hat.com>
>>
>> Entry symbols are not kprobe safe. So blacklist them for kprobing.
>>
>> Signed-off-by: Pratyush Anand <panand@...hat.com>
>
>> diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
>> index dfa1b1f..6a1292b 100644
>> --- a/arch/arm64/kernel/kprobes.c
>> +++ b/arch/arm64/kernel/kprobes.c
>> @@ -29,6 +29,7 @@
>>   #include <asm/system_misc.h>
>>   #include <asm/insn.h>
>>   #include <asm/uaccess.h>
>> +#include <asm-generic/sections.h>
>>
>>   #include "kprobes-arm64.h"
>>
>> @@ -514,6 +515,15 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
>>   	return 1;
>>   }
>>
>> +bool arch_within_kprobe_blacklist(unsigned long addr)
>> +{
>> +	return  (addr >= (unsigned long)__kprobes_text_start &&
>> +		 addr < (unsigned long)__kprobes_text_end) ||
>> +		(addr >= (unsigned long)__entry_text_start &&
>> +		 addr < (unsigned long)__entry_text_end) ||
>> +		 !!search_exception_tables(addr);
>> +}
>> +
>
> Looking at __kvm_hyp_vector, we don't have support for handling breakpoints at
> EL2, so we should forbid kprobing these address ranges too:
> __hyp_text_start -> __hyp_text_end
> __hyp_idmap_text_start -> __hyp_idmap_text_end
>
> These can probably be guarded with is_kernel_in_hyp_mode(), if this is true then
> we are running with VHE where this code runs at the same exception level as the
> rest of the kernel, so we can probe them. (In this case you may want to add
> 'eret' to aarch64_insn_is_branch() in patch 2)
>
>
> Probing things in the kernel idmap sounds dangerous! Lets blacklist that too:
> __idmap_text_start -> __idmap_text_end
>

I've made these changes.  I noticed there's no include file definitions 
for these symbols so I've added local extern declarations in 
arch_within_kprobe_blacklist().

Thanks,
-dl