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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] Some fixes to IRET hypercall and failsafe callback handlers:
# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID ae6af19f47d3805fd07f320a8d2132963768c67a
# Parent e84b1185013ff6784ce94c557ce710d78c828de0
Some fixes to IRET hypercall and failsafe callback handlers:
1. IRET hypercall must restore the event callback mask. This
was missing on x86/64, and both subarchitectures now restore
from EFLAGS.IF.
2. Failsafe callbacks are fixed to detect whether fault is due to
bad segment or due to IRET. In the latter case we now
immediatiately kill the process. This avoids infinite looping
between IRET hypercall and failsafe callback handler in the guest.
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
diff -r e84b1185013f -r ae6af19f47d3
linux-2.6-xen-sparse/arch/i386/kernel/entry-xen.S
--- a/linux-2.6-xen-sparse/arch/i386/kernel/entry-xen.S Wed Mar 29 09:46:36 2006
+++ b/linux-2.6-xen-sparse/arch/i386/kernel/entry-xen.S Wed Mar 29 11:02:45 2006
@@ -65,7 +65,6 @@
ORIG_EAX = 0x24
EIP = 0x28
CS = 0x2C
-EVENT_MASK = 0x2E
EFLAGS = 0x30
OLDESP = 0x34
OLDSS = 0x38
@@ -290,14 +289,14 @@
restore_nocheck:
#else
restore_nocheck:
- testl $(VM_MASK|NMI_MASK), EFLAGS(%esp)
+ movl EFLAGS(%esp), %eax
+ testl $(VM_MASK|NMI_MASK), %eax
jnz hypervisor_iret
- movb EVENT_MASK(%esp), %al
- notb %al # %al == ~saved_mask
+ shr $9, %eax # EAX[0] == IRET_EFLAGS.IF
GET_VCPU_INFO
andb evtchn_upcall_mask(%esi),%al
- andb $1,%al # %al == mask & ~saved_mask
- jnz restore_all_enable_events # != 0 => reenable event delivery
+ andb $1,%al # EAX[0] == IRET_EFLAGS.IF & event_mask
+ jnz restore_all_enable_events # != 0 => enable event delivery
#endif
RESTORE_REGS
addl $4, %esp
@@ -555,14 +554,9 @@
RESTORE_REGS
addl $4, %esp
1: iret
-.section .fixup,"ax"
-2: pushl $0
- pushl $do_iret_error
- jmp error_code
-.previous
.section __ex_table,"a"
.align 4
- .long 1b,2b
+ .long 1b,iret_exc
.previous
14: __DISABLE_INTERRUPTS
jmp 11b
@@ -614,30 +608,51 @@
.byte 0x00,0x00 # jmp 11b
# Hypervisor uses this for application faults while it executes.
+# We get here for two reasons:
+# 1. Fault while reloading DS, ES, FS or GS
+# 2. Fault while executing IRET
+# Category 1 we fix up by reattempting the load, and zeroing the segment
+# register if the load fails.
+# Category 2 we fix up by jumping to do_iret_error. We cannot use the
+# normal Linux return path in this case because if we use the IRET hypercall
+# to pop the stack frame we end up in an infinite loop of failsafe callbacks.
+# We distinguish between categories by maintaining a status value in EAX.
ENTRY(failsafe_callback)
-1: popl %ds
-2: popl %es
-3: popl %fs
-4: popl %gs
- subl $4,%esp
- SAVE_ALL
- jmp ret_from_exception
-.section .fixup,"ax"; \
-6: movl $0,(%esp); \
- jmp 1b; \
-7: movl $0,(%esp); \
- jmp 2b; \
-8: movl $0,(%esp); \
- jmp 3b; \
-9: movl $0,(%esp); \
- jmp 4b; \
-.previous; \
-.section __ex_table,"a";\
- .align 4; \
- .long 1b,6b; \
- .long 2b,7b; \
- .long 3b,8b; \
- .long 4b,9b; \
+ pushl %eax
+ movl $1,%eax
+1: mov 4(%esp),%ds
+2: mov 8(%esp),%es
+3: mov 12(%esp),%fs
+4: mov 16(%esp),%gs
+ testl %eax,%eax
+ popl %eax
+ jz 5f
+ addl $16,%esp # EAX != 0 => Category 2 (Bad IRET)
+ jmp iret_exc
+5: addl $16,%esp # EAX == 0 => Category 1 (Bad segment)
+ pushl $0
+ SAVE_ALL
+ jmp ret_from_exception
+.section .fixup,"ax"; \
+6: xorl %eax,%eax; \
+ movl %eax,4(%esp); \
+ jmp 1b; \
+7: xorl %eax,%eax; \
+ movl %eax,8(%esp); \
+ jmp 2b; \
+8: xorl %eax,%eax; \
+ movl %eax,12(%esp); \
+ jmp 3b; \
+9: xorl %eax,%eax; \
+ movl %eax,16(%esp); \
+ jmp 4b; \
+.previous; \
+.section __ex_table,"a"; \
+ .align 4; \
+ .long 1b,6b; \
+ .long 2b,7b; \
+ .long 3b,8b; \
+ .long 4b,9b; \
.previous
#endif
diff -r e84b1185013f -r ae6af19f47d3
linux-2.6-xen-sparse/arch/x86_64/kernel/entry-xen.S
--- a/linux-2.6-xen-sparse/arch/x86_64/kernel/entry-xen.S Wed Mar 29
09:46:36 2006
+++ b/linux-2.6-xen-sparse/arch/x86_64/kernel/entry-xen.S Wed Mar 29
11:02:45 2006
@@ -520,13 +520,13 @@
CFI_REMEMBER_STATE
jnz retint_careful
retint_restore_args:
- movb EVENT_MASK-REST_SKIP(%rsp), %al
- notb %al # %al == ~saved_mask
- XEN_GET_VCPU_INFO(%rsi)
- andb evtchn_upcall_mask(%rsi),%al
- andb $1,%al # %al == mask & ~saved_mask
- jnz restore_all_enable_events # != 0 => reenable event delivery
- XEN_PUT_VCPU_INFO(%rsi)
+ movl EFLAGS-REST_SKIP(%rsp), %eax
+ shr $9, %eax # EAX[0] == IRET_EFLAGS.IF
+ XEN_GET_VCPU_INFO(%rsi)
+ andb evtchn_upcall_mask(%rsi),%al
+ andb $1,%al # EAX[0] == IRET_EFLAGS.IF & event_mask
+ jnz restore_all_enable_events # != 0 => enable event delivery
+ XEN_PUT_VCPU_INFO(%rsi)
RESTORE_ARGS 0,8,0
HYPERVISOR_IRET 0
@@ -803,12 +803,11 @@
# So, on entry to the handler we detect whether we interrupted an
# existing activation in its critical region -- if so, we pop the current
# activation and restart the handler using the previous one.
-ENTRY(do_hypervisor_callback) # do_hyperviosr_callback(struct *pt_regs)
+ENTRY(do_hypervisor_callback) # do_hypervisor_callback(struct *pt_regs)
# Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will
# see the correct pointer to the pt_regs
movq %rdi, %rsp # we don't return, adjust the stack frame
-11: movb $0, EVENT_MASK(%rdi)
- movq %gs:pda_irqstackptr,%rax
+11: movq %gs:pda_irqstackptr,%rax
incl %gs:pda_irqcount
cmovzq %rax,%rsp
pushq %rdi
@@ -853,15 +852,44 @@
# When the kernel is interrupted in the critical section, the kernel
# will do IRET in that case, and everything will be restored at that point,
# i.e. it just resumes from the next instruction interrupted with the same
context.
-
+
# Hypervisor uses this for application faults while it executes.
-# Unlike i386 there is no need to reload the saved segment selectors:
-# Xen already reloaded all valid ones and zeroed the others.
+# We get here for two reasons:
+# 1. Fault while reloading DS, ES, FS or GS
+# 2. Fault while executing IRET
+# Category 1 we do not need to fix up as Xen has already reloaded all segment
+# registers that could be reloaded and zeroed the others.
+# Category 2 we fix up by killing the current process. We cannot use the
+# normal Linux return path in this case because if we use the IRET hypercall
+# to pop the stack frame we end up in an infinite loop of failsafe callbacks.
+# We distinguish between categories by comparing each saved segment register
+# with its current contents: any discrepancy means we in category 1.
ENTRY(failsafe_callback)
- addq $0x30,%rsp /* skip %rcx,%r11,%ds,%es,%fs,%gs */
+ movw %ds,%cx
+ cmpw %cx,0x10(%rsp)
+ jne 1f
+ movw %es,%cx
+ cmpw %cx,0x18(%rsp)
+ jne 1f
+ movw %fs,%cx
+ cmpw %cx,0x20(%rsp)
+ jne 1f
+ movw %gs,%cx
+ cmpw %cx,0x28(%rsp)
+ jne 1f
+ /* All segments match their saved values => Category 2 (Bad IRET). */
+ movq (%rsp),%rcx
+ movq 8(%rsp),%r11
+ addq $0x30,%rsp
+ movq $-9999,%rdi /* better code? */
+ jmp do_exit
+1: /* Segment mismatch => Category 1 (Bad segment). Retry the IRET. */
+ movq (%rsp),%rcx
+ movq 8(%rsp),%r11
+ addq $0x30,%rsp
+ pushq $0
SAVE_ALL
- jmp error_exit
-
+ jmp error_exit
#if 0
.section __ex_table,"a"
.align 8
diff -r e84b1185013f -r ae6af19f47d3
linux-2.6-xen-sparse/arch/x86_64/kernel/xen_entry.S
--- a/linux-2.6-xen-sparse/arch/x86_64/kernel/xen_entry.S Wed Mar 29
09:46:36 2006
+++ b/linux-2.6-xen-sparse/arch/x86_64/kernel/xen_entry.S Wed Mar 29
11:02:45 2006
@@ -2,7 +2,7 @@
* Copied from arch/xen/i386/kernel/entry.S
*/
/* Offsets into shared_info_t. */
-#define evtchn_upcall_pending 0
+#define evtchn_upcall_pending /* 0 */
#define evtchn_upcall_mask 1
#define sizeof_vcpu_shift 6
@@ -35,7 +35,6 @@
XEN_PUT_VCPU_INFO(reg)
#define XEN_TEST_PENDING(reg) testb $0xFF,evtchn_upcall_pending(reg)
-EVENT_MASK = (CS+4)
VGCF_IN_SYSCALL = (1<<8)
diff -r e84b1185013f -r ae6af19f47d3 xen/arch/x86/x86_32/asm-offsets.c
--- a/xen/arch/x86/x86_32/asm-offsets.c Wed Mar 29 09:46:36 2006
+++ b/xen/arch/x86/x86_32/asm-offsets.c Wed Mar 29 11:02:45 2006
@@ -44,7 +44,6 @@
OFFSET(UREGS_eflags, struct cpu_user_regs, eflags);
OFFSET(UREGS_error_code, struct cpu_user_regs, error_code);
OFFSET(UREGS_entry_vector, struct cpu_user_regs, entry_vector);
- OFFSET(UREGS_saved_upcall_mask, struct cpu_user_regs, saved_upcall_mask);
OFFSET(UREGS_kernel_sizeof, struct cpu_user_regs, esp);
DEFINE(UREGS_user_sizeof, sizeof(struct cpu_user_regs));
BLANK();
diff -r e84b1185013f -r ae6af19f47d3 xen/arch/x86/x86_32/traps.c
--- a/xen/arch/x86/x86_32/traps.c Wed Mar 29 09:46:36 2006
+++ b/xen/arch/x86/x86_32/traps.c Wed Mar 29 11:02:45 2006
@@ -230,8 +230,8 @@
/* No longer in NMI context. */
clear_bit(_VCPUF_nmi_masked, ¤t->vcpu_flags);
- /* Restore upcall mask from saved value. */
- current->vcpu_info->evtchn_upcall_mask = regs->saved_upcall_mask;
+ /* Restore upcall mask from supplied EFLAGS.IF. */
+ current->vcpu_info->evtchn_upcall_mask = !(eflags & X86_EFLAGS_IF);
/*
* The hypercall exit path will overwrite EAX with this return
diff -r e84b1185013f -r ae6af19f47d3 xen/arch/x86/x86_64/asm-offsets.c
--- a/xen/arch/x86/x86_64/asm-offsets.c Wed Mar 29 09:46:36 2006
+++ b/xen/arch/x86/x86_64/asm-offsets.c Wed Mar 29 11:02:45 2006
@@ -48,7 +48,6 @@
OFFSET(UREGS_eflags, struct cpu_user_regs, eflags);
OFFSET(UREGS_rsp, struct cpu_user_regs, rsp);
OFFSET(UREGS_ss, struct cpu_user_regs, ss);
- OFFSET(UREGS_saved_upcall_mask, struct cpu_user_regs, saved_upcall_mask);
OFFSET(UREGS_kernel_sizeof, struct cpu_user_regs, es);
DEFINE(UREGS_user_sizeof, sizeof(struct cpu_user_regs));
BLANK();
diff -r e84b1185013f -r ae6af19f47d3 xen/arch/x86/x86_64/traps.c
--- a/xen/arch/x86/x86_64/traps.c Wed Mar 29 09:46:36 2006
+++ b/xen/arch/x86/x86_64/traps.c Wed Mar 29 11:02:45 2006
@@ -210,6 +210,9 @@
/* No longer in NMI context. */
clear_bit(_VCPUF_nmi_masked, ¤t->vcpu_flags);
+ /* Restore upcall mask from supplied EFLAGS.IF. */
+ current->vcpu_info->evtchn_upcall_mask = !(iret_saved.rflags & EF_IE);
+
/* Saved %rax gets written back to regs->rax in entry.S. */
return iret_saved.rax;
}
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