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Message-ID: <ad614e86-7e39-e9b7-4a8f-3ea1f5a7b61d@linux.intel.com>
Date: Thu, 29 Mar 2018 06:51:23 -0700
From: Dave Hansen <dave.hansen@...ux.intel.com>
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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 03/28/2018 11:58 PM, Alexander Popov wrote:
>> 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.
Oh, and since there's no 32-bit trampoline stack, we don't need it on
32-bit?
If end up reposting this set again, could you add a few comments about
this around the ERASE_KSTACK macro definitions, or perhaps the call
sites? You might even want to call them ERASE_KSTACK_CLOBBER (for
32-bit) and ERASE_KSTACK_NOCLOBBER (for 64-bit) to make this more clear.
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