From: Jan Beulich <jbeulich@suse.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: lkml <linux-kernel@vger.kernel.org>
Subject: [PATCH] x86/stackframe/32: repair 32-bit Xen PV
Date: Mon, 7 Oct 2019 12:41:41 +0200 [thread overview]
Message-ID: <ef1c9381-dfc7-7150-feca-581f4d798513@suse.com> (raw)
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 just in case.
Fixes: 3c88c692c287 ("x86/stackframe/32: Provide consistent pt_regs")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -48,6 +48,17 @@
#include "calling.h"
+#ifndef CONFIG_XEN_PV
+# define USER_SEGMENT_RPL_MASK SEGMENT_RPL_MASK
+#else
+/*
+ * When running paravirtualized on Xen the kernel runs in ring 1, and hence
+ * simple mask based tests (i.e. ones not comparing against USER_RPL) have to
+ * ignore bit 0. See also the C-level get_kernel_rpl().
+ */
+# define USER_SEGMENT_RPL_MASK (SEGMENT_RPL_MASK & ~1)
+#endif
+
.section .entry.text, "ax"
/*
@@ -172,7 +183,7 @@
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 +228,7 @@
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)
next reply other threads:[~2019-10-07 10:41 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-07 10:41 Jan Beulich [this message]
2019-10-24 7:40 ` Ping: [PATCH] x86/stackframe/32: repair 32-bit Xen PV Jan Beulich
2019-10-24 16:11 ` Andy Lutomirski
2019-10-24 16:31 ` [Xen-devel] " Andrew Cooper
2019-10-24 16:33 ` Andy Lutomirski
2019-10-25 6:06 ` Jan Beulich
2019-10-25 6:09 ` Jürgen Groß
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