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Message-ID: <CABCJKue27Aba_MJqB68Bh282zyL=LSQSBXV5TAb-NfsOAqJRnQ@mail.gmail.com>
Date: Fri, 18 Oct 2019 10:35:49 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Mark Rutland <mark.rutland@....com>
Cc: Jann Horn <jannh@...gle.com>, Will Deacon <will@...nel.org>,
Catalin Marinas <catalin.marinas@....com>, Steven Rostedt <rostedt@...dmis.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, Dave Martin <Dave.Martin@....com>,
Kees Cook <keescook@...omium.org>, Laura Abbott <labbott@...hat.com>,
Nick Desaulniers <ndesaulniers@...gle.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>,
kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 18/18] arm64: implement Shadow Call Stack
On Fri, Oct 18, 2019 at 10:23 AM Mark Rutland <mark.rutland@....com> wrote:
> I think scs_save() would better live in assembly in cpu_switch_to(),
> where we switch the stack and current. It shouldn't matter whether
> scs_load() is inlined or not, since the x18 value _should_ be invariant
> from the PoV of the task.
Note that there's also a call to scs_save in cpu_die, because the
current task's shadow stack pointer is only stored in x18 and we don't
want to lose it.
> We just need to add a TSK_TI_SCS to asm-offsets.c, and then insert a
> single LDR at the end:
>
> mov sp, x9
> msr sp_el0, x1
> #ifdef CONFIG_SHADOW_CALL_STACK
> ldr x18, [x1, TSK_TI_SCS]
> #endif
> ret
TSK_TI_SCS is already defined, so yes, we could move this to
cpu_switch_to. I would still prefer to have the overflow check that's
in scs_thread_switch though.
Sami
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