From: Michal Luczaj <mhal@xxxxxxx>
Introduce ASM_TRY_FEP() to allow using the try-catch method to handle
exceptions that occur on forced emulation. ASM_TRY() 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
due to KVM advancing RIP to skip the prefix and the exception ends up
unhandled.
Signed-off-by: Michal Luczaj <mhal@xxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
lib/x86/desc.h | 13 ++++++++++---
x86/emulator.c | 1 -
x86/pmu.c | 1 -
3 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index 10ba8cb..8f708fd 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -92,13 +92,20 @@ typedef struct __attribute__((packed)) {
u16 iomap_base;
} tss64_t;
-#define ASM_TRY(catch) \
- "movl $0, %%gs:4 \n\t" \
- ".pushsection .data.ex \n\t" \
+#define __ASM_TRY(prefix, catch) \
+ "movl $0, %%gs:4\n\t" \
+ ".pushsection .data.ex\n\t" \
__ASM_SEL(.long, .quad) " 1111f, " catch "\n\t" \
".popsection \n\t" \
+ prefix "\n\t" \
"1111:"
+#define ASM_TRY(catch) __ASM_TRY("", catch)
+
+/* 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)
+
/*
* selector 32-bit 64-bit
* 0x00 NULL descriptor NULL descriptor
diff --git a/x86/emulator.c b/x86/emulator.c
index 769a049..6dc88f1 100644
--- a/x86/emulator.c
+++ b/x86/emulator.c
@@ -18,7 +18,6 @@
static int exceptions;
/* Forced emulation prefix, used to invoke the emulator unconditionally. */
-#define KVM_FEP "ud2; .byte 'k', 'v', 'm';"
#define KVM_FEP_LENGTH 5
static int fep_available = 1;
diff --git a/x86/pmu.c b/x86/pmu.c
index 01be1e9..457c5b9 100644
--- a/x86/pmu.c
+++ b/x86/pmu.c
@@ -33,7 +33,6 @@
#define N 1000000
-#define KVM_FEP "ud2; .byte 'k', 'v', 'm';"
// These values match the number of instructions and branches in the
// assembly block in check_emulated_instr().
#define EXPECTED_INSTR 17
--
2.37.1.559.g78731f0fdb-goog
