linux-kernel - Re: [PATCH] ARM: fault: Implement copy_from_kernel_nofault

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Date: Tue, 23 Jan 2024 19:02:23 +0000
From: Mark Brown <broonie@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Russell King <linux@...linux.org.uk>, Ard Biesheuvel <ardb@...nel.org>,
	Wang Kefeng <wangkefeng.wang@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ben Hutchings <ben@...adent.org.uk>,
	linux-arm-kernel@...ts.infradead.org,
	"Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ARM: fault: Implement copy_from_kernel_nofault_allowed()

On Mon, Jan 22, 2024 at 05:12:38PM -0800, Kees Cook wrote:
> Under PAN emulation when dumping backtraces from things like the
> LKDTM EXEC_USERSPACE test[1], a double fault (which would hang a CPU)
> would happen because of dump_instr() attempting to read a userspace
> address. Make sure copy_from_kernel_nofault() does not attempt this
> any more.

This appears to fix the original issue:

   https://lava.sirena.org.uk/scheduler/job/497571

(though so did your earlier patch) so:

Tested-by: Mark Brown <broonie@...nel.org>

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