From 8dbd9966f82f95b017f06e9397fc78064b688d61 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Mon, 28 Apr 2025 09:48:14 +0200 Subject: [PATCH] x86: constrain sub-page access length in mmio_ro_emulated_write() Without doing so we could trigger the ASSERT_UNREACHABLE() in subpage_mmio_write_emulate(). A comment there actually says this validation would already have been done ... Fixes: 8847d6e23f97 ("x86/mm: add API for marking only part of a MMIO page read only") Signed-off-by: Jan Beulich Reviewed-by: Jason Andryuk --- xen/arch/x86/mm.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index 1cf2365167..ac5b51d17a 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -5195,8 +5195,13 @@ int cf_check mmio_ro_emulated_write( return X86EMUL_UNHANDLEABLE; } - subpage_mmio_write_emulate(mmio_ro_ctxt->mfn, PAGE_OFFSET(offset), - p_data, bytes); + if ( bytes <= 8 ) + subpage_mmio_write_emulate(mmio_ro_ctxt->mfn, PAGE_OFFSET(offset), + p_data, bytes); + else if ( subpage_mmio_find_page(mmio_ro_ctxt->mfn) ) + gprintk(XENLOG_WARNING, + "unsupported %u-byte write to R/O MMIO 0x%"PRI_mfn"%03lx\n", + bytes, mfn_x(mmio_ro_ctxt->mfn), PAGE_OFFSET(offset)); return X86EMUL_OKAY; } -- 2.39.5