linux-kernel - Re: [RFC PATCH] arm64: fix the missing ktpi= cmdline check in arm64_kernel_unmapped_at

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Message-ID: <20200317121050.GH8831@lakrids.cambridge.arm.com>
Date:   Tue, 17 Mar 2020 12:10:51 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Hongbo Yao <yaohongbo@...wei.com>
Cc:     will@...nel.org, broonie@...nel.org, linux-kernel@...r.kernel.org,
        catalin.marinas@....com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH] arm64: fix the missing ktpi= cmdline check in
 arm64_kernel_unmapped_at_el0()

[Adding Catalin and LAKML]

Mark.

On Tue, Mar 17, 2020 at 07:47:08PM +0800, Hongbo Yao wrote:
> Kpti cannot be disabled from the kernel cmdline after the commit
> 09e3c22a("arm64: Use a variable to store non-global mappings decision").
> 
> Bring back the missing check of kpti= command-line option to fix the
> case where the SPE driver complains the missing "kpti-off" even it has
> already been set.
> 
> Signed-off-by: Hongbo Yao <yaohongbo@...wei.com>
> ---
>  arch/arm64/include/asm/mmu.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
> index 3c9533322558..ebbc0d3ac2f7 100644
> --- a/arch/arm64/include/asm/mmu.h
> +++ b/arch/arm64/include/asm/mmu.h
> @@ -34,7 +34,8 @@ extern bool arm64_use_ng_mappings;
>  
>  static inline bool arm64_kernel_unmapped_at_el0(void)
>  {
> -	return arm64_use_ng_mappings;
> +	return arm64_use_ng_mappings &&
> +		cpus_have_const_cap(ARM64_UNMAP_KERNEL_AT_EL0);
>  }
>  
>  typedef void (*bp_hardening_cb_t)(void);
> -- 
> 2.20.1
>