From 7fe9f5366bd5d7ee3cfd9f66868a4410d6e4792d Mon Sep 17 00:00:00 2001 From: MJ Pooladkhay Date: Mon, 22 Dec 2025 17:42:07 +0000 Subject: [PATCH] KVM: selftests: Fix sign extension bug in get_desc64_base() The function get_desc64_base() performs a series of bitwise left shifts on fields of various sizes. More specifically, when performing '<< 24' on 'desc->base2' (which is a u8), 'base2' is promoted to a signed integer before shifting. In a scenario where base2 >= 0x80, the shift places a 1 into bit 31, causing the 32-bit intermediate value to become negative. When this result is cast to uint64_t or ORed into the return value, sign extension occurs, corrupting the upper 32 bits of the address (base3). Example: Given: base0 = 0x5000 base1 = 0xd6 base2 = 0xf8 base3 = 0xfffffe7c Expected return: 0xfffffe7cf8d65000 Actual return: 0xfffffffff8d65000 Fix this by explicitly casting the fields to 'uint64_t' before shifting to prevent sign extension. Signed-off-by: MJ Pooladkhay Link: https://patch.msgid.link/20251222174207.107331-1-mj@pooladkhay.com Signed-off-by: Sean Christopherson --- tools/testing/selftests/kvm/include/x86/processor.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h index 57d62a425109b..26a91bb73c93a 100644 --- a/tools/testing/selftests/kvm/include/x86/processor.h +++ b/tools/testing/selftests/kvm/include/x86/processor.h @@ -436,8 +436,10 @@ struct kvm_x86_state { static inline uint64_t get_desc64_base(const struct desc64 *desc) { - return ((uint64_t)desc->base3 << 32) | - (desc->base0 | ((desc->base1) << 16) | ((desc->base2) << 24)); + return (uint64_t)desc->base3 << 32 | + (uint64_t)desc->base2 << 24 | + (uint64_t)desc->base1 << 16 | + (uint64_t)desc->base0; } static inline uint64_t rdtsc(void) -- 2.47.3