linux-kernel - Re: [PATCH v2 1/3] x86/bugs: Only harden syscalls when needed

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Date: Mon, 15 Apr 2024 08:47:48 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Nikolay Borisov <nik.borisov@...e.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org, linux-kernel@...r.kernel.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>, 
	KP Singh <kpsingh@...nel.org>, Waiman Long <longman@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v2 1/3] x86/bugs: Only harden syscalls when needed

On Mon, 15 Apr 2024 at 08:27, Nikolay Borisov <nik.borisov@...e.com> wrote:
>
> Same as with every issue - assess the problem and develop fixes.

No. Let's have at least all the infrastructure in place to be a bit proactive.

> Let's be honest, the indirect branches in the syscall handler aren't the
> biggest problem

Oh, they have been.

> it's the stacked LSMs.

Hopefully those will get fixed too.

There's a few other fairly reachable ones (the timer indirection ones
are much too close, and VFS file ops aren't entirely out of reach).

But maybe some day we'll be in a situation where it's actually fairly
hard to reach indirect kernel calls from untrusted user space.

The system call ones are pretty much always the first ones, though.

> And even if those get fixes
> chances are the security people will likely find some other avenue of
> attack, I think even now the attack is somewhat hard to pull off.

No disagreement about that. I think outright sw bugs are still the
99.9% thing. But let's learn from history instead of "assess the
problem" every time anew.

               Linus