From 7d7f11008918255dab8f845b3a74698fae304605 Mon Sep 17 00:00:00 2001 From: bluhm Date: Thu, 6 Jun 2024 00:36:46 +0000 Subject: [PATCH] Clear DF flag after kcopy faulted. A memory corruption in the kernel happend that was caused by memset in the wrong direction. After that DF bit was set in ddb rflags. Only kcopy and memmove use std to set DF bit. kcopy has the special property that it can fault. In this case DF is set in the trap frame. kpageflttrap() changes the return address to copy_fault via pcb_onfault. When alltraps_kern returns, it restores the rflags with DF set and jumps into copy_fault. From there a function return goes back into regular kernel execution. Now DF is set, but kernel memset and memcpy expect that it is cleared. After copy fault, also reset the DF bit with cld in copy_fault. The crash happend on OpenBSD 7.4 amd64. As i386 code looks similar, also insert cld there. OK guenther@ miod@ --- sys/arch/amd64/amd64/copy.S | 3 ++- sys/arch/i386/i386/locore.s | 3 ++- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/sys/arch/amd64/amd64/copy.S b/sys/arch/amd64/amd64/copy.S index f09ebf929b2..23f5f70220f 100644 --- a/sys/arch/amd64/amd64/copy.S +++ b/sys/arch/amd64/amd64/copy.S @@ -1,4 +1,4 @@ -/* $OpenBSD: copy.S,v 1.19 2023/07/28 06:18:35 guenther Exp $ */ +/* $OpenBSD: copy.S,v 1.20 2024/06/06 00:36:46 bluhm Exp $ */ /* $NetBSD: copy.S,v 1.1 2003/04/26 18:39:26 fvdl Exp $ */ /* @@ -189,6 +189,7 @@ ENTRY(_copyin) NENTRY(copy_fault) DECLARE_ONFAULT(copy_fault) + cld SMAP_CLAC movq CPUVAR(CURPCB),%rdx popq PCB_ONFAULT(%rdx) diff --git a/sys/arch/i386/i386/locore.s b/sys/arch/i386/i386/locore.s index b25acfaab5c..feb8fa4edae 100644 --- a/sys/arch/i386/i386/locore.s +++ b/sys/arch/i386/i386/locore.s @@ -1,4 +1,4 @@ -/* $OpenBSD: locore.s,v 1.204 2023/12/12 07:37:20 deraadt Exp $ */ +/* $OpenBSD: locore.s,v 1.205 2024/06/06 00:36:46 bluhm Exp $ */ /* $NetBSD: locore.s,v 1.145 1996/05/03 19:41:19 christos Exp $ */ /*- @@ -555,6 +555,7 @@ ENTRY(_copyin) ret ENTRY(copy_fault) + cld SMAP_CLAC GET_CURPCB(%edx) popl PCB_ONFAULT(%edx) -- 2.20.1