From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
TRY_ASM() mishandles exceptions thrown by the forced-emulation-triggered
emulator. While the faulting address stored in the exception table points
at forced emulation prefix, when an exceptions comes, RIP is 5 bytes
(size of KVM_FEP) ahead and the exception ends up unhandled.
Signed-off-by: Michal Luczaj <mhal@xxxxxxx>
---
For the sake of completeness, I've added `prefix` to 32-bit __TRY_ASM()
as well.
lib/x86/desc.h | 8 ++++++--
x86/emulator.c | 1 +
2 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index 2a285eb..8854fcc 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -81,21 +81,25 @@ typedef struct __attribute__((packed)) {
} tss64_t;
#ifdef __x86_64
-#define ASM_TRY(catch) \
+#define __ASM_TRY(prefix, catch) \
"movl $0, %%gs:4 \n\t" \
".pushsection .data.ex \n\t" \
".quad 1111f, " catch "\n\t" \
".popsection \n\t" \
+ prefix \
"1111:"
#else
-#define ASM_TRY(catch) \
+#define __ASM_TRY(prefix, catch) \
"movl $0, %%gs:4 \n\t" \
".pushsection .data.ex \n\t" \
".long 1111f, " catch "\n\t" \
".popsection \n\t" \
+ prefix \
"1111:"
#endif
+#define ASM_TRY(catch) __ASM_TRY("", catch)
+
/*
* selector 32-bit 64-bit
* 0x00 NULL descriptor NULL descriptor
diff --git a/x86/emulator.c b/x86/emulator.c
index 96d3ccd..0eb7c1a 100644
--- a/x86/emulator.c
+++ b/x86/emulator.c
@@ -19,6 +19,7 @@ static int exceptions;
/* Forced emulation prefix, used to invoke the emulator unconditionally. */
#define KVM_FEP "ud2; .byte 'k', 'v', 'm';"
+#define ASM_TRY_FEP(catch) __ASM_TRY(KVM_FEP, catch)
struct regs {
u64 rax, rbx, rcx, rdx;
--
2.37.1
