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Date: Fri, 26 Apr 2013 15:15:10 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Borislav Petkov <bp@...en8.de>
CC: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
x86@...nel.org, Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
Matthew Garrett <mjg@...hat.com>,
Matt Fleming <matt.fleming@...el.com>,
Eric Northup <digitaleric@...gle.com>,
Dan Rosenberg <drosenberg@...curity.com>,
Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 6/6] x86: kaslr: report kernel offset on panic
On 04/26/2013 03:13 PM, Borislav Petkov wrote:
> On Fri, Apr 26, 2013 at 12:03:25PM -0700, Kees Cook wrote:
>> When the system panics, include the kernel offset in the report to assist
>> in debugging.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>> arch/x86/kernel/setup.c | 24 ++++++++++++++++++++++++
>> 1 file changed, 24 insertions(+)
>>
>> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
>> index fae9134..95a33b1 100644
>> --- a/arch/x86/kernel/setup.c
>> +++ b/arch/x86/kernel/setup.c
>> @@ -830,6 +830,18 @@ static void __init trim_low_memory_range(void)
>> }
>>
>> /*
>> + * Dump out kernel offset information on panic.
>> + */
>> +static int
>> +dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
>> +{
>> + pr_emerg("Kernel Offset: 0x%lx\n",
>> + (unsigned long)&_text - __START_KERNEL);
>
> So what's wrong with subtracting the offset from the function addresses
> on the stack so that traces can show the addresses as they are in
> vmlinux, completely agnostic of any randomization?
>
That really makes it harder to figure out what the heck the register
content may mean...
-hpa
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