The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From feb8e960d780e170e992a70491eec9dd68f4dbf2 Mon Sep 17 00:00:00 2001

From: Christophe Leroy christophe.leroy@c-s.fr Date: Fri, 17 Apr 2020 11:58:36 +0000 Subject: [PATCH] powerpc/mm: Fix CONFIG_PPC_KUAP_DEBUG on PPC32

CONFIG_PPC_KUAP_DEBUG is not selectable because it depends on PPC_32 which doesn't exists.

Fixing it leads to a deadlock due to a vital register getting clobbered in _switch().

Change dependency to PPC32 and use r0 instead of r4 in _switch()

Fixes: e2fb9f544431 ("powerpc/32: Prepare for Kernel Userspace Access Protection") Cc: stable@vger.kernel.org # v5.2+ Signed-off-by: Christophe Leroy christophe.leroy@c-s.fr Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/540242f7d4573f7cdf1b3bf46bb35f743b2cd68f.158712465...

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S index a6371fb8f761..8420abd4ea1c 100644 --- a/arch/powerpc/kernel/entry_32.S +++ b/arch/powerpc/kernel/entry_32.S @@ -732,7 +732,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_SPE) stw r10,_CCR(r1) stw r1,KSP(r3) /* Set old stack pointer */

- kuap_check r2, r4 + kuap_check r2, r0 #ifdef CONFIG_SMP /* We need a sync somewhere here to make sure that if the * previous task gets rescheduled on another CPU, it sees all diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype index 0c3c1902135c..27a81c291be8 100644 --- a/arch/powerpc/platforms/Kconfig.cputype +++ b/arch/powerpc/platforms/Kconfig.cputype @@ -397,7 +397,7 @@ config PPC_KUAP

config PPC_KUAP_DEBUG bool "Extra debugging for Kernel Userspace Access Protection" - depends on PPC_KUAP && (PPC_RADIX_MMU || PPC_32) + depends on PPC_KUAP && (PPC_RADIX_MMU || PPC32) help Add extra debugging for Kernel Userspace Access Protection (KUAP) If you're unsure, say N.