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Date: Wed, 12 Feb 2020 12:59:22 -0800
From: Sami Tolvanen <samitolvanen@...gle.com>
To: James Morse <james.morse@....com>
Cc: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, Mark Rutland <mark.rutland@....com>,
Dave Martin <Dave.Martin@....com>, Kees Cook <keescook@...omium.org>,
Laura Abbott <labbott@...hat.com>, Marc Zyngier <maz@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>, Jann Horn <jannh@...gle.com>,
Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 11/11] arm64: scs: add shadow stacks for SDEI
On Tue, Feb 11, 2020 at 5:57 AM James Morse <james.morse@....com> wrote:
>
> Hi Sami,
>
> On 28/01/2020 18:49, Sami Tolvanen wrote:
> > This change adds per-CPU shadow call stacks for the SDEI handler.
> > Similarly to how the kernel stacks are handled, we add separate shadow
> > stacks for normal and critical events.
>
> Reviewed-by: James Morse <james.morse@....com>
> Tested-by: James Morse <james.morse@....com>
Thank you for taking the time to test this, James!
> > diff --git a/arch/arm64/kernel/scs.c b/arch/arm64/kernel/scs.c
> > index eaadf5430baa..dddb7c56518b 100644
> > --- a/arch/arm64/kernel/scs.c
> > +++ b/arch/arm64/kernel/scs.c
>
> > +static int scs_alloc_percpu(unsigned long * __percpu *ptr, int cpu)
> > +{
> > + unsigned long *p;
> > +
> > + p = __vmalloc_node_range(PAGE_SIZE, SCS_SIZE,
> > + VMALLOC_START, VMALLOC_END,
> > + GFP_SCS, PAGE_KERNEL,
> > + 0, cpu_to_node(cpu),
> > + __builtin_return_address(0));
>
> (What makes this arch specific? arm64 has its own calls like this for the regular vmap
> stacks because it plays tricks with the alignment. Here the alignment requirement comes
> from the core SCS code... Would another architecture implement these
> scs_alloc_percpu()/scs_free_percpu() differently?)
You are correct, these aren't necessarily specific to arm64. However,
right now, we are not allocating per-CPU shadow stacks anywhere else,
so this was a natural place for the helper functions. Would you prefer
me to move these to kernel/scs.c instead?
Sami
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