From: "tip-bot2 for Jan Beulich" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Jan Beulich <jbeulich@suse.com>, <stable@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
Brian Gerst <brgerst@gmail.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org
Subject: [tip: x86/urgent] x86/stackframe/32: Repair 32-bit Xen PV
Date: Tue, 19 Nov 2019 10:12:12 -0000 [thread overview]
Message-ID: <157415833282.12247.2847277914358020515.tip-bot2@tip-bot2> (raw)
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 189eb7f3d7ec70ceeaa195221ddfd95016e10ace
Gitweb: https://git.kernel.org/tip/189eb7f3d7ec70ceeaa195221ddfd95016e10ace
Author: Jan Beulich <jbeulich@suse.com>
AuthorDate: Mon, 18 Nov 2019 16:21:12 +01:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 19 Nov 2019 09:01:59 +01:00
x86/stackframe/32: Repair 32-bit Xen PV
Once again RPL checks have been introduced which don't account for a
32-bit kernel living in ring 1 when running in a PV Xen domain. The
case in FIXUP_FRAME has been preventing boot. Adjust BUG_IF_WRONG_CR3
as well to guard against future uses of the macro on a code path
reachable when running in PV mode under Xen; I have to admit that I
stopped at a certain point trying to figure out whether there are
present ones.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: <stable@vger.kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel@lists.xenproject.org <xen-devel@lists.xenproject.org>
Fixes: 3c88c692c287 ("x86/stackframe/32: Provide consistent pt_regs")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/entry/entry_32.S | 4 ++--
arch/x86/include/asm/segment.h | 12 ++++++++++++
2 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index f83ca5a..3f847d8 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -172,7 +172,7 @@
ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
.if \no_user_check == 0
/* coming from usermode? */
- testl $SEGMENT_RPL_MASK, PT_CS(%esp)
+ testl $USER_SEGMENT_RPL_MASK, PT_CS(%esp)
jz .Lend_\@
.endif
/* On user-cr3? */
@@ -217,7 +217,7 @@
testl $X86_EFLAGS_VM, 4*4(%esp)
jnz .Lfrom_usermode_no_fixup_\@
#endif
- testl $SEGMENT_RPL_MASK, 3*4(%esp)
+ testl $USER_SEGMENT_RPL_MASK, 3*4(%esp)
jnz .Lfrom_usermode_no_fixup_\@
orl $CS_FROM_KERNEL, 3*4(%esp)
diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
index ac38929..6669164 100644
--- a/arch/x86/include/asm/segment.h
+++ b/arch/x86/include/asm/segment.h
@@ -31,6 +31,18 @@
*/
#define SEGMENT_RPL_MASK 0x3
+/*
+ * When running on Xen PV, the actual privilege level of the kernel is 1,
+ * not 0. Testing the Requested Privilege Level in a segment selector to
+ * determine whether the context is user mode or kernel mode with
+ * SEGMENT_RPL_MASK is wrong because the PV kernel's privilege level
+ * matches the 0x3 mask.
+ *
+ * Testing with USER_SEGMENT_RPL_MASK is valid for both native and Xen PV
+ * kernels because privilege level 2 is never used.
+ */
+#define USER_SEGMENT_RPL_MASK 0x2
+
/* User mode is privilege level 3: */
#define USER_RPL 0x3
next reply other threads:[~2019-11-19 10:12 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-19 10:12 tip-bot2 for Jan Beulich [this message]
[not found] <0fad341f-b7f5-f859-d55d-f0084ee7087e@suse.com>
2019-11-19 21:01 ` [tip: x86/urgent] x86/stackframe/32: Repair 32-bit Xen PV tip-bot2 for Jan Beulich
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