Using assembler trampolines instead of && fixes NMI IRET test.
There is another bug, however. Returns to the same privilege level do
not pop SS:RSP on 32-bit, so the nested NMI underflowed the stack at "s".
This is fixed in the new code. The new code doesn't set up SS:RSP and
instead leaves some space for the nested NMI handler on the alternate
stack. The old stack pointer is kept and restored when the nested
handler returns.
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
x86/eventinj.c | 64 ++++++++++++++++++++++++++++++++++++++--------------------
1 file changed, 42 insertions(+), 22 deletions(-)
diff --git a/x86/eventinj.c b/x86/eventinj.c
index 2124bdf..1df3a43 100644
--- a/x86/eventinj.c
+++ b/x86/eventinj.c
@@ -59,17 +59,25 @@ static volatile int test_count;
ulong stack_phys;
void *stack_va;
-static void pf_tss(void)
+void do_pf_tss(void)
{
-start:
printf("PF running\n");
install_pte(phys_to_virt(read_cr3()), 1, stack_va,
stack_phys | PTE_PRESENT | PTE_WRITE, 0);
invlpg(stack_va);
- asm volatile ("iret");
- goto start;
}
+extern void pf_tss(void);
+
+asm (
+ "pf_tss: \n\t"
+ "call do_pf_tss \n\t"
+ "add $"S", %"R "sp\n\t" // discard error code
+ "iret"W" \n\t"
+ "jmp pf_tss\n\t"
+ );
+
+
static void of_isr(struct ex_regs *r)
{
printf("OF isr running\n");
@@ -114,39 +122,51 @@ static void nmi_isr(struct ex_regs *r)
printf("After nested NMI to self\n");
}
-unsigned long after_iret_addr;
+unsigned long *iret_stack;
static void nested_nmi_iret_isr(struct ex_regs *r)
{
printf("Nested NMI isr running rip=%x\n", r->rip);
- if (r->rip == after_iret_addr)
+ if (r->rip == iret_stack[-3])
test_count++;
}
+
+extern void do_iret(ulong phys_stack, void *virt_stack);
+
+// Return to same privilege level won't pop SS or SP, so
+// save it in RDX while we run on the nested stack
+
+asm("do_iret:"
+#ifdef __x86_64__
+ "mov %rdi, %rax \n\t" // phys_stack
+ "mov %rsi, %rdx \n\t" // virt_stack
+#else
+ "mov 4(%esp), %eax \n\t" // phys_stack
+ "mov 8(%esp), %edx \n\t" // virt_stack
+#endif
+ "xchg %"R "dx, %"R "sp \n\t" // point to new stack
+ "pushf"W" \n\t"
+ "mov %cs, %ecx \n\t"
+ "push"W" %"R "cx \n\t"
+ "push"W" $1f \n\t"
+ "outl %eax, $0xe4 \n\t" // flush page
+ "iret"W" \n\t"
+ "1: xchg %"R "dx, %"R "sp \n\t" // point to old stack
+ "ret\n\t"
+ );
+
static void nmi_iret_isr(struct ex_regs *r)
{
unsigned long *s = alloc_page();
test_count++;
- printf("NMI isr running %p stack %p\n", &&after_iret, s);
+ printf("NMI isr running stack %p\n", s);
handle_exception(2, nested_nmi_iret_isr);
printf("Sending nested NMI to self\n");
apic_self_nmi();
printf("After nested NMI to self\n");
- s[4] = read_ss();
- s[3] = 0; /* rsp */
- s[2] = read_rflags();
- s[1] = read_cs();
- s[0] = after_iret_addr = (unsigned long)&&after_iret;
- asm ("mov %%" R "sp, %0\n\t"
- "mov %1, %%" R "sp\n\t"
- "outl %2, $0xe4\n\t" /* flush stack page */
-#ifdef __x86_64__
- "iretq\n\t"
-#else
- "iretl\n\t"
-#endif
- : "=m"(s[3]) : "rm"(&s[0]), "a"((unsigned int)virt_to_phys(s)) : "memory");
-after_iret:
+ iret_stack = &s[128];
+ do_iret(virt_to_phys(s), iret_stack);
printf("After iret\n");
}
--
1.8.3.1
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