From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Thu, 19 Jan 2017 15:40:08 +0000 Subject: [PATCH] arm64: avoid returning from bad_mode In-Reply-To: <1484760221-30205-1-git-send-email-mark.rutland@arm.com> References: <1484760221-30205-1-git-send-email-mark.rutland@arm.com> Message-ID: <20170119154008.GC21809@e104818-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Jan 18, 2017 at 05:23:41PM +0000, Mark Rutland wrote: > Generally, taking an unexpected exception should be a fatal event, and > bad_mode is intended to cater for this. However, it should be possible > to contain unexpected synchronous exceptions from EL0 without bringing > the kernel down, by sending a SIGILL to the task. > > We tried to apply this approach in commit 9955ac47f4ba1c95 ("arm64: > don't kill the kernel on a bad esr from el0"), by sending a signal for > any bad_mode call resulting from an EL0 exception. > > However, this also applies to other unexpected exceptions, such as > SError and FIQ. The entry paths for these exceptions branch to bad_mode > without configuring the link register, and have no kernel_exit. Thus, if > we take one of these exceptions from EL0, bad_mode will eventually > return to the original user link register value. > > This patch fixes this by introducing a new bad_el0_sync handler to cater > for the recoverable case, and restoring bad_mode to its original state, > whereby it calls panic() and never returns. The recoverable case > branches to bad_el0_sync with a bl, and returns to userspace via the > usual ret_to_user mechanism. > > Signed-off-by: Mark Rutland > Fixes: 9955ac47f4ba1c95 ("arm64: don't kill the kernel on a bad esr from el0") > Reported-by: Mark Salter > Cc: Catalin Marinas > Cc: Will Deacon > Cc: stable at vger.kernel.org Thanks. I'll queue this for 4.10. -- Catalin