Re: [PATCH 3/3] mm: Care about shadow stack guard gap when getting an unmapped area

From: Deepak Gupta <debug@rivosinc.com>
To: Mark Brown <broonie@kernel.org>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Richard Henderson <richard.henderson@linaro.org>,
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Subject: Re: [PATCH 3/3] mm: Care about shadow stack guard gap when getting an unmapped area
Date: Wed, 4 Sep 2024 12:07:12 -0700	[thread overview]
Message-ID: <Ztiv4NtsIkKnyiLO@debug.ba.rivosinc.com> (raw)
In-Reply-To: <dbaf5653-df46-4e17-bce1-aec7fb168197@sirena.org.uk>

On Tue, Sep 03, 2024 at 08:57:20PM +0100, Mark Brown wrote:
>On Tue, Sep 03, 2024 at 03:41:49PM -0400, Liam R. Howlett wrote:
>> * Mark Brown <broonie@kernel.org> [240902 15:09]:
>
>> > +static inline unsigned long stack_guard_placement(vm_flags_t vm_flags)
>> > +{
>> > +	if (vm_flags & VM_SHADOW_STACK)
>> > +		return PAGE_SIZE;
>
>> Is PAGE_SIZE is enough?
>
>It's what x86 currently uses so it'll be no worse off if it gets moved
>to the generic code (there's a comment in the arch code explaing what's
>needed there) and it's enough for arm64, we only do single record
>pushes/pops or (optionally) writes to unconstrained addresses.

It's enough for RISC-V too.