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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: 3c88c692c2 ("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
This commit is contained in:
Jan Beulich 2019-11-18 16:21:12 +01:00 committed by Thomas Gleixner
parent af42d3466b
commit 81ff2c37f9
2 changed files with 14 additions and 2 deletions
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4
arch/x86/entry/entry_32.S
View File

@ -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)

12
arch/x86/include/asm/segment.h
View File

@ -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