linux-kernel - Re: [patch V3 64/66] x86/fpu: Return proper error codes from user access functions

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Date:   Wed, 23 Jun 2021 12:56:43 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...e.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [patch V3 64/66] x86/fpu: Return proper error codes from user access functions

On Wed, Jun 23 2021 at 10:30, Borislav Petkov wrote:
>> +/* Returns 0 or the negated trap number, which results in -EFAULT for #PF */
>>  #define user_insn(insn, output, input...)				\
>>  ({									\
>>  	int err;							\
>> @@ -94,14 +95,14 @@ static inline void fpstate_init_soft(str
>>  	might_fault();							\
>>  									\
>>  	asm volatile(ASM_STAC "\n"					\
>> -		     "1:" #insn "\n\t"					\
>> +		     "1: " #insn "\n"					\
>>  		     "2: " ASM_CLAC "\n"				\
>>  		     ".section .fixup,\"ax\"\n"				\
>> -		     "3:  movl $-1,%[err]\n"				\
>> +		     "3:  negl %%eax\n"					\
>>  		     "    jmp  2b\n"					\
>>  		     ".previous\n"					\
>> -		     _ASM_EXTABLE(1b, 3b)				\
>> -		     : [err] "=r" (err), output				\
>> +		     _ASM_EXTABLE_FAULT(1b, 3b)				\
>> +		     : [err] "=a" (err), output				\
>>  		     : "0"(0), input);					\
>>  	err;								\
>
> Don't we wanna do the same for XSTATE_OP() too?
>
> Because restore_hwregs_from_user() could call
> xrstor_from_user_sigframe() too which ends up doing XRSTOR and latter
> can cause a #PF too.

Bah, right you are.