From aec196ba2affa5b396ed1bc16340067d66972f24 Mon Sep 17 00:00:00 2001 From: Haotian Jiang Date: Thu, 6 Aug 2026 10:06:01 -0700 Subject: [PATCH] KVM: TDX: Reject INIT_MEM_REGION if number of bytes would overflow a u64 The nr_pages field in struct kvm_tdx_init_mem_region is a u64 that comes directly from userspace via copy_from_user(). The current validation uses a manual overflow check: region.gpa + (region.nr_pages << PAGE_SHIFT) <= region.gpa When nr_pages >= 2^52, the shift (nr_pages << PAGE_SHIFT) wraps around to a small value, bypassing the wrap check. While downstream protections (gfn_to_memslot() returning NULL for GFNs outside any memslot, and kvm_slot_has_gmem() checking for NULL) prevent any actual out-of-bounds access, the overflow itself is a real bug that should be caught at the validation layer. Replace the manual overflow check with check_shl_overflow() to correctly detect the wrap-around. Note, the manual wrap-around check on the gpa+size technically has a benign off-by-one bug, and can also use check_add_overflow(). Those flaws will be addressed shortly. Opportunistically separate the initial sanity checks from the more involved checks to try and make the code easier to read. Fixes: c846b451d3c5 ("KVM: TDX: Add an ioctl to create initial guest memory") Reported-by: Sashiko Bot Closes: https://lore.kernel.org/all/20260630214952.98C851F000E9@smtp.kernel.org Cc: Yan Zhao Cc: Binbin Wu Cc: Ackerley Tng Signed-off-by: Haotian Jiang [sean: use gpa_t, isolate check_shl_overflow() change, tweak changelog] Reviewed-by: Binbin Wu Reviewed-by: Yan Zhao Tested-by: Yan Zhao Link: https://patch.msgid.link/20260806170602.4112602-2-seanjc@google.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/vmx/tdx.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index 53fd4e63ce40..d991996259a8 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -3257,6 +3257,7 @@ static int tdx_vcpu_init_mem_region(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *c struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm); struct kvm_tdx_init_mem_region region; struct tdx_gmem_post_populate_arg arg; + gpa_t nr_bytes; long gmem_ret; int ret; @@ -3274,10 +3275,13 @@ static int tdx_vcpu_init_mem_region(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *c return -EFAULT; if (!PAGE_ALIGNED(region.source_addr) || !region.source_addr || - !PAGE_ALIGNED(region.gpa) || !region.nr_pages || - region.gpa + (region.nr_pages << PAGE_SHIFT) <= region.gpa || + !PAGE_ALIGNED(region.gpa) || !region.nr_pages) + return -EINVAL; + + if (check_shl_overflow(region.nr_pages, PAGE_SHIFT, &nr_bytes) || + region.gpa + nr_bytes <= region.gpa || !vt_is_tdx_private_gpa(kvm, region.gpa) || - !vt_is_tdx_private_gpa(kvm, region.gpa + (region.nr_pages << PAGE_SHIFT) - 1)) + !vt_is_tdx_private_gpa(kvm, region.gpa + nr_bytes - 1)) return -EINVAL; ret = 0;