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: 3c88c692c2 ("x86/stackframe/32: Provide consistent pt_regs")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Stable Team <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/32d8713d-25a7-84ab-b74b-aa3e88abce6b@suse.com
alistair/sunxi64-5.5-dsi
Jan Beulich
Thomas Gleixner
parent
81ff2c37f9
commit
29b810f5a5
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@ -1341,11 +1341,6 @@ END(spurious_interrupt_bug)
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#ifdef CONFIG_XEN_PV
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ENTRY(xen_hypervisor_callback)
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pushl $-1 /* orig_ax = -1 => not a system call */
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SAVE_ALL
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ENCODE_FRAME_POINTER
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TRACE_IRQS_OFF
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/*
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* Check to see if we got the event in the critical
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* region in xen_iret_direct, after we've reenabled
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@ -1353,16 +1348,17 @@ ENTRY(xen_hypervisor_callback)
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* iret instruction's behaviour where it delivers a
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* pending interrupt when enabling interrupts:
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*/
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movl PT_EIP(%esp), %eax
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cmpl $xen_iret_start_crit, %eax
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cmpl $xen_iret_start_crit, (%esp)
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jb 1f
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cmpl $xen_iret_end_crit, %eax
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cmpl $xen_iret_end_crit, (%esp)
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jae 1f
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jmp xen_iret_crit_fixup
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ENTRY(xen_do_upcall)
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1: mov %esp, %eax
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call xen_iret_crit_fixup
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1:
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pushl $-1 /* orig_ax = -1 => not a system call */
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SAVE_ALL
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ENCODE_FRAME_POINTER
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TRACE_IRQS_OFF
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mov %esp, %eax
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call xen_evtchn_do_upcall
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#ifndef CONFIG_PREEMPTION
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call xen_maybe_preempt_hcall
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@ -126,10 +126,9 @@ hyper_iret:
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.globl xen_iret_start_crit, xen_iret_end_crit
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/*
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* This is called by xen_hypervisor_callback in entry.S when it sees
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* This is called by xen_hypervisor_callback in entry_32.S when it sees
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* that the EIP at the time of interrupt was between
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* xen_iret_start_crit and xen_iret_end_crit. We're passed the EIP in
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* %eax so we can do a more refined determination of what to do.
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* xen_iret_start_crit and xen_iret_end_crit.
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*
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* The stack format at this point is:
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* ----------------
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@ -138,34 +137,23 @@ hyper_iret:
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* eflags } outer exception info
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* cs }
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* eip }
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* ---------------- <- edi (copy dest)
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* ----------------
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* eax : outer eax if it hasn't been restored
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* ----------------
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* eflags } nested exception info
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* cs } (no ss/esp because we're nested
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* eip } from the same ring)
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* orig_eax }<- esi (copy src)
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* - - - - - - - -
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* fs }
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* es }
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* ds } SAVE_ALL state
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* eax }
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* : :
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* ebx }<- esp
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* ----------------
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* eflags }
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* cs } nested exception info
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* eip }
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* return address : (into xen_hypervisor_callback)
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*
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* In order to deliver the nested exception properly, we need to shift
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* everything from the return addr up to the error code so it sits
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* just under the outer exception info. This means that when we
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* handle the exception, we do it in the context of the outer
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* exception rather than starting a new one.
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* In order to deliver the nested exception properly, we need to discard the
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* nested exception frame such that when we handle the exception, we do it
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* in the context of the outer exception rather than starting a new one.
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*
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* The only caveat is that if the outer eax hasn't been restored yet
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* (ie, it's still on stack), we need to insert its value into the
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* SAVE_ALL state before going on, since it's usermode state which we
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* eventually need to restore.
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* The only caveat is that if the outer eax hasn't been restored yet (i.e.
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* it's still on stack), we need to restore its value here.
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*/
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ENTRY(xen_iret_crit_fixup)
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pushl %ecx
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/*
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* Paranoia: Make sure we're really coming from kernel space.
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* One could imagine a case where userspace jumps into the
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@ -176,32 +164,26 @@ ENTRY(xen_iret_crit_fixup)
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* jump instruction itself, not the destination, but some
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* virtual environments get this wrong.
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*/
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movl PT_CS(%esp), %ecx
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movl 3*4(%esp), %ecx /* nested CS */
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andl $SEGMENT_RPL_MASK, %ecx
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cmpl $USER_RPL, %ecx
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popl %ecx
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je 2f
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lea PT_ORIG_EAX(%esp), %esi
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lea PT_EFLAGS(%esp), %edi
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/*
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* If eip is before iret_restore_end then stack
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* hasn't been restored yet.
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*/
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cmp $iret_restore_end, %eax
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cmpl $iret_restore_end, 1*4(%esp)
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jae 1f
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movl 0+4(%edi), %eax /* copy EAX (just above top of frame) */
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movl %eax, PT_EAX(%esp)
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movl 4*4(%esp), %eax /* load outer EAX */
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ret $4*4 /* discard nested EIP, CS, and EFLAGS as
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* well as the just restored EAX */
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lea ESP_OFFSET(%edi), %edi /* move dest up over saved regs */
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/* set up the copy */
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1: std
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mov $PT_EIP / 4, %ecx /* saved regs up to orig_eax */
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rep movsl
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cld
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lea 4(%edi), %esp /* point esp to new frame */
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2: jmp xen_do_upcall
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1:
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ret $3*4 /* discard nested EIP, CS, and EFLAGS */
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2:
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ret
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END(xen_iret_crit_fixup)
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