On Wed, Jul 12, 2023 at 08:55:21PM +1200, Kai Huang wrote: > @@ -72,7 +142,46 @@ > movq %r9, TDX_MODULE_r9(%rsi) > movq %r10, TDX_MODULE_r10(%rsi) > movq %r11, TDX_MODULE_r11(%rsi) > - .endif > + .endif /* \ret */ > + > + .if \saved > + .if \ret && \host > + /* > + * Clear registers shared by guest for VP.ENTER to prevent > + * speculative use of guest's values, including those are > + * restored from the stack. > + * > + * See arch/x86/kvm/vmx/vmenter.S: > + * > + * In theory, a L1 cache miss when restoring register from stack > + * could lead to speculative execution with guest's values. > + * > + * Note: RBP/RSP are not used as shared register. RSI has been > + * restored already. > + * > + * XOR is cheap, thus unconditionally do for all leafs. > + */ > + xorq %rcx, %rcx > + xorq %rdx, %rdx > + xorq %r8, %r8 > + xorq %r9, %r9 > + xorq %r10, %r10 > + xorq %r11, %r11 > + xorq %r12, %r12 > + xorq %r13, %r13 > + xorq %r14, %r14 > + xorq %r15, %r15 > + xorq %rbx, %rbx ^ those are an instant pop below, seems daft to clear them. > + xorq %rdi, %rdi > + .endif /* \ret && \host */ > + > + /* Restore callee-saved GPRs as mandated by the x86_64 ABI */ > + popq %r15 > + popq %r14 > + popq %r13 > + popq %r12 > + popq %rbx > + .endif /* \saved */ > > FRAME_END > RET > -- > 2.41.0 >
