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authorJan Beulich <jbeulich@suse.com>2019-11-18 16:21:12 +0100
committerThomas Gleixner <tglx@linutronix.de>2019-11-19 21:58:28 +0100
commit81ff2c37f9e5d77593928df0536d86443195fd64 (patch)
treeb3c5ddb89e3740c3cbd640f3f98517f5d4becb33 /arch/x86
parentaf42d3466bdc8f39806b26f593604fdc54140bcb (diff)
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. Fixes: 3c88c692c287 ("x86/stackframe/32: Provide consistent pt_regs") Signed-off-by: Jan Beulich <jbeulich@suse.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Stable Team <stable@vger.kernel.org> Link: https://lore.kernel.org/r/0fad341f-b7f5-f859-d55d-f0084ee7087e@suse.com
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/entry/entry_32.S4
-rw-r--r--arch/x86/include/asm/segment.h12
2 files changed, 14 insertions, 2 deletions
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index f83ca5aa8b77..3f847d843e47 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 ac3892920419..6669164abadc 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