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Subject: Re: [PATCH v7 11/11] arm64: scs: add shadow stacks for SDEI
To:     Sami Tolvanen <samitolvanen@google.com>
Cc:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Kees Cook <keescook@chromium.org>,
        Laura Abbott <labbott@redhat.com>,
        Marc Zyngier <maz@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Jann Horn <jannh@google.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        clang-built-linux@googlegroups.com,
        kernel-hardening@lists.openwall.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20191018161033.261971-1-samitolvanen@google.com>
 <20200128184934.77625-1-samitolvanen@google.com>
 <20200128184934.77625-12-samitolvanen@google.com>
From:   James Morse <james.morse@arm.com>
Message-ID: <dbb090ae-d1ec-cb1a-0710-e1d3cfe762b9@arm.com>
Date:   Tue, 11 Feb 2020 13:57:29 +0000
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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@arm.com>
Tested-by: James Morse <james.morse@arm.com>


> 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?)


Thanks,

James