Fixed two problems:
1) Output operands with the '=' constraint are dead-on-arrival.
Thus gcc was free to ignore the fail = 0 initialization. Since
the asm only set fail when vm{launch,resume} exited early, fail
was technically undefined when vm{launch,resume} entered the
guest! Using the '+' constraint instead tells gcc the value is
live.
2) On early vm{launch,resume} failure, the 'setbe %0' instruction
was running with the guest's GPRs since SAVE_GPR_C hadn't
run yet. Since %0 is typically replaced with OFFSET(%%rbp),
some arbitrary guest stack memory is modified. Solution is
to restore the host's registers before using any asm code
generated by gcc.
Signed-off-by: Peter Feiner <pfeiner@xxxxxxxxxx>
---
x86/vmx.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/x86/vmx.c b/x86/vmx.c
index 107a005..b2e015f 100644
--- a/x86/vmx.c
+++ b/x86/vmx.c
@@ -925,11 +925,14 @@ static int vmx_run()
"1: "
"vmresume\n\t"
"2: "
+ SAVE_GPR_C
"setbe %0\n\t"
+ "jmp 3f\n\t"
"vmx_return:\n\t"
SAVE_GPR_C
+ "3: \n\t"
SAVE_RFLAGS
- : "=m"(fail)
+ : "+m"(fail)
: "m"(launched), "i"(HOST_RSP)
: "rdi", "rsi", "memory", "cc"
--
2.8.0.rc3.226.g39d4020
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