linux-kernel - Re: [PATCH 5/7] x86/bugs: Only harden syscalls when needed

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Message-ID: <20240411153841.zexbsqrdli54kiez@treble>
Date: Thu, 11 Apr 2024 08:38:41 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Andrew Cooper <andrew.cooper3@...rix.com>
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>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	KP Singh <kpsingh@...nel.org>, Waiman Long <longman@...hat.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 5/7] x86/bugs: Only harden syscalls when needed

On Thu, Apr 11, 2024 at 11:06:37AM +0100, Andrew Cooper wrote:
> > +#define __do_syscall(table, func_direct, nr, regs)			\
> > +({									\
> > +	unsigned long __rax, __rdi, __rsi;				\
> > +									\
> > +	asm_inline volatile(						\
> > +		ALTERNATIVE("call " __stringify(func_direct) "\n\t",	\
> > +			    ANNOTATE_RETPOLINE_SAFE			\
> > +			    "call *%[func_ptr]\n\t",			\
> 
> This wants to be a plain maybe-thunk'd indirect call, and without the
> ANNOTATE_RETPOLINE_SAFE.
> 
> Or you're going to get into cases where some combinations of command
> line options do unexpected things e.g. retpolining everything except the
> syscall dispatch.

In that case won't X86_FEATURE_INDIRECT_SAFE get cleared, resulting in
the above using a direct call?  Or did I miss something?

-- 
Josh