linux-kernel - Re: [PATCH v2 26/39] x86/cet/shstk: Introduce routines modifying shstk

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <1d9c6497405eb66f687f7f640b33f5c61e62b83a.camel@intel.com>
Date:   Thu, 20 Oct 2022 21:51:55 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "bsingharora@...il.com" <bsingharora@...il.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "Syromiatnikov, Eugene" <esyr@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "Eranian, Stephane" <eranian@...gle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "fweimer@...hat.com" <fweimer@...hat.com>,
        "nadav.amit@...il.com" <nadav.amit@...il.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "dethoma@...rosoft.com" <dethoma@...rosoft.com>,
        "kcc@...gle.com" <kcc@...gle.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "oleg@...hat.com" <oleg@...hat.com>,
        "Yang, Weijiang" <weijiang.yang@...el.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "Moreira, Joao" <joao.moreira@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "pavel@....cz" <pavel@....cz>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "john.allen@....com" <john.allen@....com>,
        "rppt@...nel.org" <rppt@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "corbet@....net" <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "gorcunov@...il.com" <gorcunov@...il.com>
CC:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v2 26/39] x86/cet/shstk: Introduce routines modifying
 shstk

On Wed, 2022-10-05 at 22:58 +0000, Andrew Cooper wrote:
> On 05/10/2022 23:47, Edgecombe, Rick P wrote:
> > On Wed, 2022-10-05 at 02:43 +0000, Andrew Cooper wrote:
> > > On 29/09/2022 23:29, Rick Edgecombe wrote:
> > > > diff --git a/arch/x86/include/asm/special_insns.h
> > > > b/arch/x86/include/asm/special_insns.h
> > > > index 35f709f619fb..f096f52bd059 100644
> > > > --- a/arch/x86/include/asm/special_insns.h
> > > > +++ b/arch/x86/include/asm/special_insns.h
> > > > @@ -223,6 +223,19 @@ static inline void clwb(volatile void
> > > > *__p)
> > > >                 : [pax] "a" (p));
> > > >    }
> > > >    
> > > > +#ifdef CONFIG_X86_SHADOW_STACK
> > > > +static inline int write_user_shstk_64(u64 __user *addr, u64
> > > > val)
> > > > +{
> > > > +     asm_volatile_goto("1: wrussq %[val], (%[addr])\n"
> > > > +                       _ASM_EXTABLE(1b, %l[fail])
> > > > +                       :: [addr] "r" (addr), [val] "r" (val)
> > > > +                       :: fail);
> > > 
> > > "1: wrssq %[val], %[addr]\n"
> > > _ASM_EXTABLE(1b, %l[fail])
> > > : [addr] "+m" (*addr)
> > > : [val] "r" (val)
> > > :: fail
> > > 
> > > Otherwise you've failed to tell the compiler that you wrote to
> > > *addr.
> > > 
> > > With that fixed, it's not volatile because there are no
> > > unexpressed
> > > side
> > > effects.
> > 
> > Ok, thanks!
> 
> On further consideration, it should be "=m" not "+m", which is even
> less
> constrained, and even easier for an enterprising optimiser to try and
> do
> something useful with.

AFAICT this won't work on all gccs. Asm goto's used to not support
having outputs. They are also implicitly volatile anyway. So I think
I'll have to leave it. But I can change the wrss one in the selftest to
"=m".