From aee101d7b95a03078945681dd7f7ea5e4a1e7686 Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Mon, 17 Jan 2022 23:44:03 +1000
Subject: [PATCH] powerpc/64s: Mask SRR0 before checking against the masked NIP
References: bsc#1194869
Patch-mainline: v5.17 or v5.17-rc2 (next release)
Git-commit: aee101d7b95a03078945681dd7f7ea5e4a1e7686
Commit 314f6c23dd8d ("powerpc/64s: Mask NIP before checking against
SRR0") masked off the low 2 bits of the NIP value in the interrupt
stack frame in case they are non-zero and mis-compare against a SRR0
register value of a CPU which always reads back 0 from the 2 low bits
which are reserved.
This now causes the opposite problem that an implementation which does
implement those bits in SRR0 will mis-compare against the masked NIP
value in which they have been cleared. QEMU is one such implementation,
and this is allowed by the architecture.
This can be triggered by sigfuz by setting low bits of PT_NIP in the
signal context.
Fix this for now by masking the SRR0 bits as well. Cleaner is probably
to sanitise these values before putting them in registers or stack, but
this is the quick and backportable fix.
Fixes: 314f6c23dd8d ("powerpc/64s: Mask NIP before checking against SRR0")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220117134403.2995059-1-npiggin@gmail.com
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/kernel/interrupt_64.S | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
index 92088f848266..7bab2d7de372 100644
--- a/arch/powerpc/kernel/interrupt_64.S
+++ b/arch/powerpc/kernel/interrupt_64.S
@@ -30,6 +30,7 @@ COMPAT_SYS_CALL_TABLE:
.ifc \srr,srr
mfspr r11,SPRN_SRR0
ld r12,_NIP(r1)
+ clrrdi r11,r11,2
clrrdi r12,r12,2
100: tdne r11,r12
EMIT_WARN_ENTRY 100b,__FILE__,__LINE__,(BUGFLAG_WARNING | BUGFLAG_ONCE)
@@ -40,6 +41,7 @@ COMPAT_SYS_CALL_TABLE:
.else
mfspr r11,SPRN_HSRR0
ld r12,_NIP(r1)
+ clrrdi r11,r11,2
clrrdi r12,r12,2
100: tdne r11,r12
EMIT_WARN_ENTRY 100b,__FILE__,__LINE__,(BUGFLAG_WARNING | BUGFLAG_ONCE)
--
2.31.1