On 05.02.25 10:54, Jan Beulich wrote:
On 05.02.2025 10:10, Juergen Gross wrote:xen_hypercall_hvm(), which is used when running as a Xen PVH guest at most only once during early boot, is clobbering %rbx. Depending on whether the caller relies on %rbx to be preserved across the call or not, this clobbering might result in an early crash of the system.This can be avoided by not modifying %rbx in xen_hypercall_hvm(). Fixes: b4845bb63838 ("x86/xen: add central hypercall functions") Signed-off-by: Juergen Gross <[email protected]> --- arch/x86/xen/xen-head.S | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S index 9252652afe59..4378b817ed32 100644 --- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -117,8 +117,7 @@ SYM_FUNC_START(xen_hypercall_hvm) pop %ebx pop %eax #else - lea xen_hypercall_amd(%rip), %rbx - cmp %rax, %rbxThere's no memory access here, but ...+ cmp xen_hypercall_amd(%rip), %rax... you now read from memory here. That can't be right. Afaict the original use of LEA needs to stay, just with a different scratch register.
Oh, right. Thanks for noticing. Juergen
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