linux-kernel - Re: [PATCH v3 27/37] x86/shstk: Introduce routines modifying shstk

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Date:   Wed, 16 Nov 2022 22:38:19 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "peterz@...radead.org" <peterz@...radead.org>
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Subject: Re: [PATCH v3 27/37] x86/shstk: Introduce routines modifying shstk

On Wed, 2022-11-16 at 11:18 +0100, Peter Zijlstra wrote:
> > > 
> > > Should you write a 64bit value even if the task receiving a
> > > signal is
> > > 32bit ?
> > 
> > 32 bit support was also dropped.
> 
> How? Task could start life as 64bit, frob LDT to set up 32bit code
> segment and jump into it and start doing 32bit syscalls, then what?
> 
> AFAICT those 32bit syscalls will end up doing SA_IA32_ABI sigframes.

Hmm, good point. This series used to support normal 32 bit apps via
ia32 emulation which would have handled this. But I removed it (blocked
in the enabling logic) because it didn't seem like it would get enough
use to justify the extra code. That doesn't block this scenario here
though.

Pardon the possibly naive question, but is this 32/64 bit mixing
something any normal, shstk-desiring, applications would actually do? O
r more that they could do?

Thanks,

Rick