# Commit eb7cd0593d88c4b967a24bca8bd30591966676cd # Date 2024-09-12 09:13:04 +0200 # Author Jan Beulich # Committer Jan Beulich x86/HVM: properly reject "indirect" VRAM writes While ->count will only be different from 1 for "indirect" (data in guest memory) accesses, it being 1 does not exclude the request being an "indirect" one. Check both to be on the safe side, and bring the ->count part also in line with what ioreq_send_buffered() actually refuses to handle. Fixes: 3bbaaec09b1b ("x86/hvm: unify stdvga mmio intercept with standard mmio intercept") Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper --- a/xen/arch/x86/hvm/stdvga.c +++ b/xen/arch/x86/hvm/stdvga.c @@ -530,14 +530,14 @@ static bool cf_check stdvga_mem_accept( spin_lock(&s->lock); - if ( p->dir == IOREQ_WRITE && p->count > 1 ) + if ( p->dir == IOREQ_WRITE && (p->data_is_ptr || p->count != 1) ) { /* * We cannot return X86EMUL_UNHANDLEABLE on anything other then the * first cycle of an I/O. So, since we cannot guarantee to always be * able to send buffered writes, we have to reject any multi-cycle - * I/O and, since we are rejecting an I/O, we must invalidate the - * cache. + * or "indirect" I/O and, since we are rejecting an I/O, we must + * invalidate the cache. * Single-cycle write transactions are accepted even if the cache is * not active since we can assert, when in stdvga mode, that writes * to VRAM have no side effect and thus we can try to buffer them.