linux-kernel - Re: [PATCH v3] x86/bugs: Only harden syscalls when needed

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Date: Wed, 17 Apr 2024 16:57:38 +0200
From: Borislav Petkov <bp@...en8.de>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexandre Chartre <alexandre.chartre@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	KP Singh <kpsingh@...nel.org>, Waiman Long <longman@...hat.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v3] x86/bugs: Only harden syscalls when needed

On Tue, Apr 16, 2024 at 04:02:21PM -0700, Josh Poimboeuf wrote:
> Syscall hardening (i.e., converting the syscall indirect branch to a
> series of direct branches) may cause performance regressions in certain
> scenarios.  Only use the syscall hardening when indirect branches are
> considered unsafe.
> 
> Fixes: 1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system calls")
> Reviewed-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
> v3:
> - fix X86_FEATURE_INDIRECT_SAFE value
> 
>  arch/x86/entry/common.c            | 15 ++++++++++++---
>  arch/x86/entry/syscall_32.c        | 11 +----------
>  arch/x86/entry/syscall_64.c        |  6 ------
>  arch/x86/entry/syscall_x32.c       |  7 ++++++-
>  arch/x86/include/asm/cpufeatures.h |  1 +
>  arch/x86/include/asm/syscall.h     |  8 +++++++-
>  arch/x86/kernel/cpu/bugs.c         | 31 +++++++++++++++++++++++++++++-
>  7 files changed, 57 insertions(+), 22 deletions(-)

I poked at this a bit and can't find anything that I can complain about
so

Acked-by: Borislav Petkov (AMD) <bp@...en8.de>

I'll pick it up into urgent if no one complains soon.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette