A simple fix for a null pointer dereference in vmx_vcpu_run() with an ugly-but-safe prereq patch.
The fix also has a wart/hack where it marks RSP as clobbered using ASM_CALL_CONSTRAINT to workaround an issue where the VM-Exit label isn't found by _something_ during modpost. I vaguely recall seeing the same issue when I first worked on this code a few years back. I think it was objtool that was confused, but I can't remember the details for the life of me. I don't have more cycles to throw at deciphering the thing, and marking RSP as clobbered is safe, so I went with the hack.
Alternatively, reverting the offending commit (added in v4.19.119) would fix the immediate issue, but RDX and RSI technically need to be marked as clobbered even though it's extremely unlikely the compiler will consume their bad value. All of the above ugliness seems preferable to leaving a known bug in place.
Sean Christopherson (2): KVM: VMX: Explicitly reference RCX as the vmx_vcpu pointer in asm blobs KVM: VMX: Mark RCX, RDX and RSI as clobbered in vmx_vcpu_run()'s asm blob
arch/x86/kvm/vmx.c | 89 +++++++++++++++++++++++++--------------------- 1 file changed, 49 insertions(+), 40 deletions(-)