linux-kernel - Re: [PATCH] x86/uapi: fix SHADOW_STACK_SET

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Date:   Mon, 23 Oct 2023 23:11:18 +0300
From:   "Dmitry V. Levin" <ldv@...ace.io>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     dave.hansen@...ux.intel.com, bp@...en8.de, x86@...nel.org,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/uapi: fix SHADOW_STACK_SET_TOKEN type

On Mon, Oct 23, 2023 at 04:36:48PM +0000, Edgecombe, Rick P wrote:
> On Mon, 2023-10-23 at 01:21 +0300, Dmitry V. Levin wrote:
> > Fix the type of SHADOW_STACK_SET_TOKEN to match the type of the
> > corresponding "flags" argument of map_shadow_stack syscall which
> > is of type "unsigned int".
> > 
> > Fixes: c35559f94ebc3 ("x86/shstk: Introduce map_shadow_stack
> > syscall")
> > Signed-off-by: Dmitry V. Levin <ldv@...ace.io>
> > ---
> >  arch/x86/include/uapi/asm/mman.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/include/uapi/asm/mman.h
> > b/arch/x86/include/uapi/asm/mman.h
> > index 46cdc941f958..8419e25bb617 100644
> > --- a/arch/x86/include/uapi/asm/mman.h
> > +++ b/arch/x86/include/uapi/asm/mman.h
> > @@ -6,7 +6,7 @@
> >  #define MAP_ABOVE4G    0x80            /* only map above 4GB */
> >  
> >  /* Flags for map_shadow_stack(2) */
> > -#define SHADOW_STACK_SET_TOKEN (1ULL << 0)     /* Set up a restore
> > token in the shadow stack */
> > +#define SHADOW_STACK_SET_TOKEN (1U << 0)       /* Set up a restore
> > token in the shadow stack */
> >  
> >  #include <asm-generic/mman.h>
> 
> Good point that they are mismatched. I don't remember why flags is not
> an unsigned long though. I wonder if we should quick change it to an
> unsigned long, if it's not too late. We probably won't run out of
> flags, but maybe some value could get stuffed in the upper bits or
> something someday.

We usually don't use unsigned long for flags because we support 32-bit
architectures.


-- 
ldv