linux-kernel - Re: [PATCH] arm64: fix cleared E0POE bit after cpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <f555454a-3eb9-4537-8f69-66ec36931966@arm.com>
Date: Wed, 7 Jan 2026 11:29:48 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, rafael@...nel.org, pavel@...nel.org,
 catalin.marinas@....com, will@...nel.org, anshuman.khandual@....com,
 ryan.roberts@....com, yang@...amperecomputing.com, joey.gouly@....com
Subject: Re: [PATCH] arm64: fix cleared E0POE bit after cpu_suspend()/resume()

On 07/01/2026 10:57, Yeoreum Yun wrote:
>>> @@ -97,8 +97,11 @@ SYM_FUNC_START(cpu_do_suspend)
>>>  	mrs	x9, mdscr_el1
>>>  	mrs	x10, oslsr_el1
>>>  	mrs	x11, sctlr_el1
>>> -	get_this_cpu_offset x12
>>> -	mrs	x13, sp_el0
>>> +alternative_if ARM64_HAS_TCR2
>>> +	mrs	x12, REG_TCR2_EL1
>>> +alternative_else_nop_endif
>>> +	get_this_cpu_offset x13
>>> +	mrs	x14, sp_el0
>>>  	stp	x2, x3, [x0]
>>>  	stp	x4, x5, [x0, #16]
>>>  	stp	x6, x7, [x0, #32]
>>> @@ -109,7 +112,7 @@ SYM_FUNC_START(cpu_do_suspend)
>>>  	 * Save x18 as it may be used as a platform register, e.g. by shadow
>>>  	 * call stack.
>>>  	 */
>>> -	str	x18, [x0, #96]
>>> +	stp	x14, x18, [x0, #96]
>> If TCR2_EL1 isn't supported, we store and reload an unused arbitrary
>> value. I think it'd be better to make it all conditional and add it at
>> the end, something like:
>>
>>     alternative_if ARM64_HAS_TCR2
>>         mrs    x2, REG_TCR2_EL1
>>         str    x2, [x0, #104]
>>     alternative_else_nop_endif
>>
>> Same idea on the resume path. This also avoids the noise of renaming
>> existing registers.
> IMHO, I think it would be better to sustain the change since
> it seems more simpler to maintain  and x12 is temporary regsiter
> so leaking whatever was in x12 does not really feel like a concern...

Leaking is not a concern, but I don't think it's really easier to
maintain. We can have all the conditional registers grouped together,
like DISR_EL1 and soon SCTLR2_EL1. This avoids renaming a bunch of
registers every time we save/restore a new register here.

- Kevin