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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH 1/2] x86/Xen/32: make xen_iret_crit_fixup independent of frame layout
Now that SS:ESP always get saved by SAVE_ALL, this also needs to be
accounted for in xen_iret_crit_fixup. Otherwise the old_ax value gets
interpreted as EFLAGS, and hence VM86 mode appears to be active all
the time, leading to random "vm86_32: no user_vm86: BAD" log messages
alongside processes randomly crashing.
Since following the previous model (sitting after SAVE_ALL) would
further complicate the code _and_ retain the dependency of
xen_iret_crit_fixup on frame manipulations done by entry_32.S, switch
things around and do the adjustment ahead of SAVE_ALL.
Fixes: 3c88c692c287 ("x86/stackframe/32: Provide consistent pt_regs")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1341,11 +1341,6 @@ END(spurious_interrupt_bug)
#ifdef CONFIG_XEN_PV
ENTRY(xen_hypervisor_callback)
- pushl $-1 /* orig_ax = -1 => not a system
call */
- SAVE_ALL
- ENCODE_FRAME_POINTER
- TRACE_IRQS_OFF
-
/*
* Check to see if we got the event in the critical
* region in xen_iret_direct, after we've reenabled
@@ -1353,16 +1348,17 @@ ENTRY(xen_hypervisor_callback)
* iret instruction's behaviour where it delivers a
* pending interrupt when enabling interrupts:
*/
- movl PT_EIP(%esp), %eax
- cmpl $xen_iret_start_crit, %eax
+ cmpl $xen_iret_start_crit, (%esp)
jb 1f
- cmpl $xen_iret_end_crit, %eax
+ cmpl $xen_iret_end_crit, (%esp)
jae 1f
-
- jmp xen_iret_crit_fixup
-
-ENTRY(xen_do_upcall)
-1: mov %esp, %eax
+ call xen_iret_crit_fixup
+1:
+ pushl $-1 /* orig_ax = -1 => not a system
call */
+ SAVE_ALL
+ ENCODE_FRAME_POINTER
+ TRACE_IRQS_OFF
+ mov %esp, %eax
call xen_evtchn_do_upcall
#ifndef CONFIG_PREEMPTION
call xen_maybe_preempt_hcall
--- a/arch/x86/xen/xen-asm_32.S
+++ b/arch/x86/xen/xen-asm_32.S
@@ -126,10 +126,9 @@ hyper_iret:
.globl xen_iret_start_crit, xen_iret_end_crit
/*
- * This is called by xen_hypervisor_callback in entry.S when it sees
+ * This is called by xen_hypervisor_callback in entry_32.S when it sees
* that the EIP at the time of interrupt was between
- * xen_iret_start_crit and xen_iret_end_crit. We're passed the EIP in
- * %eax so we can do a more refined determination of what to do.
+ * xen_iret_start_crit and xen_iret_end_crit.
*
* The stack format at this point is:
* ----------------
@@ -138,34 +137,23 @@ hyper_iret:
* eflags } outer exception info
* cs }
* eip }
- * ---------------- <- edi (copy dest)
- * eax : outer eax if it hasn't been restored
* ----------------
- * eflags } nested exception info
- * cs } (no ss/esp because we're nested
- * eip } from the same ring)
- * orig_eax }<- esi (copy src)
- * - - - - - - - -
- * fs }
- * es }
- * ds } SAVE_ALL state
- * eax }
- * : :
- * ebx }<- esp
+ * eax : outer eax if it hasn't been restored
* ----------------
+ * eflags }
+ * cs } nested exception info
+ * eip }
+ * return address : (into xen_hypervisor_callback)
*
- * In order to deliver the nested exception properly, we need to shift
- * everything from the return addr up to the error code so it sits
- * just under the outer exception info. This means that when we
- * handle the exception, we do it in the context of the outer
- * exception rather than starting a new one.
+ * In order to deliver the nested exception properly, we need to discard the
+ * nested exception frame such that when we handle the exception, we do it
+ * in the context of the outer exception rather than starting a new one.
*
- * The only caveat is that if the outer eax hasn't been restored yet
- * (ie, it's still on stack), we need to insert its value into the
- * SAVE_ALL state before going on, since it's usermode state which we
- * eventually need to restore.
+ * The only caveat is that if the outer eax hasn't been restored yet (i.e.
+ * it's still on stack), we need to restore its value here.
*/
ENTRY(xen_iret_crit_fixup)
+ pushl %ecx
/*
* Paranoia: Make sure we're really coming from kernel space.
* One could imagine a case where userspace jumps into the
@@ -176,32 +164,26 @@ ENTRY(xen_iret_crit_fixup)
* jump instruction itself, not the destination, but some
* virtual environments get this wrong.
*/
- movl PT_CS(%esp), %ecx
+ movl 3*4(%esp), %ecx /* nested CS */
andl $SEGMENT_RPL_MASK, %ecx
cmpl $USER_RPL, %ecx
+ popl %ecx
je 2f
- lea PT_ORIG_EAX(%esp), %esi
- lea PT_EFLAGS(%esp), %edi
-
/*
* If eip is before iret_restore_end then stack
* hasn't been restored yet.
*/
- cmp $iret_restore_end, %eax
+ cmpl $iret_restore_end, 1*4(%esp)
jae 1f
- movl 0+4(%edi), %eax /* copy EAX (just above top of frame) */
- movl %eax, PT_EAX(%esp)
-
- lea ESP_OFFSET(%edi), %edi /* move dest up over saved regs */
-
- /* set up the copy */
-1: std
- mov $PT_EIP / 4, %ecx /* saved regs up to orig_eax */
- rep movsl
- cld
-
- lea 4(%edi), %esp /* point esp to new frame */
-2: jmp xen_do_upcall
-
+ movl 4*4(%esp), %eax /* load outer EAX */
+ ret $4*4 /* discard nested EIP, CS, and EFLAGS as
+ * well as the just restored EAX */
+
+1:
+ ret $3*4 /* discard nested EIP, CS, and EFLAGS */
+
+2:
+ ret
+END(xen_iret_crit_fixup)
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