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Message-ID: <16a56461-6501-7eb9-e1a4-761c9eff9386@linux.com>
Date: Thu, 29 Mar 2018 09:58:32 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Dave Hansen <dave.hansen@...ux.intel.com>,
kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org>,
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linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v10 2/6] x86/entry: Add STACKLEAK erasing the kernel
stack at the end of syscalls
On 29.03.2018 01:55, Dave Hansen wrote:
> On 03/28/2018 12:57 PM, Alexander Popov wrote:
>> +.macro ERASE_KSTACK
>> +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
>> + PUSH_AND_CLEAR_REGS
>> + call erase_kstack
>> + POP_REGS
>> +#endif
>> +.endm
>
> Thanks again for the hard work to trim down the complexity of the
> assembly.
Hello Dave, thanks!
> I noticed the 64-bit version saves/restores registers while
> the 32-bit version doesn't. What's the reasoning there?
When erase_kstack() is called from the trampoline stack, it must save and
restore any modified registers, since all registers except RDI are live
(prepared for the userspace).
When erase_kstack() is called from the thread stack, it can clobber registers
according the function call convention without any harm.
Best regards,
Alexander
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