From 9d701bc9abaf1e9ab458545a8f320d36dc54d686 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Tue, 30 Jan 2024 18:13:14 +0000 Subject: [PATCH] x86/hvm: Fix UBSAN failure in do_hvm_op() printk Tamas reported this UBSAN failure from fuzzing: (XEN) ================================================================================ (XEN) UBSAN: Undefined behaviour in common/vsprintf.c:64:19 (XEN) negation of -9223372036854775808 cannot be represented in type 'long long int': (XEN) ----[ Xen-4.19-unstable x86_64 debug=y ubsan=y Not tainted ]---- ... (XEN) Xen call trace: (XEN) [] R ubsan.c#ubsan_epilogue+0xa/0xd9 (XEN) [] F __ubsan_handle_negate_overflow+0x99/0xce (XEN) [] F vsprintf.c#number+0x10a/0x93e (XEN) [] F vsnprintf+0x19e2/0x1c56 (XEN) [] F console.c#vprintk_common+0x76/0x34d (XEN) [] F printk+0x4d/0x4f (XEN) [] F do_hvm_op+0x288e/0x28f5 (XEN) [] F hvm_hypercall+0xad2/0x149a (XEN) [] F vmx_vmexit_handler+0x1596/0x279c (XEN) [] F vmx_asm_vmexit_handler+0xdb/0x200 The problem is an unsigned -> signed converstion because of a bad formatter (%ld trying to format an unsigned long). We could fix it by swapping to %lu, but this is a useless printk() even in debug builds, so just drop it completely. Reported-by: Tamas K Lengyel Signed-off-by: Andrew Cooper Acked-by: Jan Beulich --- xen/arch/x86/hvm/hvm.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index e3bd9157d7..e8deeb0222 100644 --- a/xen/arch/x86/hvm/hvm.c +++ b/xen/arch/x86/hvm/hvm.c @@ -5147,12 +5147,9 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg) break; default: - { - gdprintk(XENLOG_DEBUG, "Bad HVM op %ld.\n", op); rc = -ENOSYS; break; } - } if ( rc == -ERESTART ) rc = hypercall_create_continuation(__HYPERVISOR_hvm_op, "lh", -- 2.39.5