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Date: Thu, 16 Jan 2020 13:57:53 -0800
From: Sami Tolvanen <>
To: Will Deacon <>
Cc: Catalin Marinas <>, Steven Rostedt <>, 
	Masami Hiramatsu <>, Ard Biesheuvel <>, 
	Mark Rutland <>, Dave Martin <>, 
	Kees Cook <>, Laura Abbott <>, 
	Marc Zyngier <>, Nick Desaulniers <>, Jann Horn <>, 
	Miguel Ojeda <>, 
	Masahiro Yamada <>, 
	clang-built-linux <>, 
	Kernel Hardening <>, 
	linux-arm-kernel <>, LKML <>
Subject: Re: [PATCH v6 14/15] arm64: implement Shadow Call Stack

On Thu, Jan 16, 2020 at 10:24 AM Will Deacon <> wrote:
> >       .macro  irq_stack_entry
> >       mov     x19, sp                 // preserve the original sp
> > +     mov     x20, x18                // preserve the original shadow stack
> > +#endif
> Hmm, not sure about corrupting x20 here. Doesn't it hold the PMR value from
> kernel_entry?

You're right, and it's used in el1_irq after irq_handler if
CONFIG_ARM64_PSEUDO_NMI is enabled. Thanks for pointing this out.
Looks like one of x24-x29 should be safe here, and the comment needs
to be updated to explain why x20-x23 shouldn't be corrupted.


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