From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4ABCD39A048 for ; Thu, 16 Apr 2026 23:10:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776381051; cv=none; b=sqDZ8+aQMxKHH6ZR2EL/zVyISi+RoOVPDjrf0GtNf8q7CPn5V6dkdIc3FLSrI5AyvAgTUAyI1B5IsWmIYN5qOuIilaOPTftxkZAIdyoAMMdHAq+vwqy6KVNvaAMjpsajFiDgW6Skd8VOCqqK3H317pI/CL1jZ0yFaXJRsx/4t8o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776381051; c=relaxed/simple; bh=9rNPGkTreelzLILSOGZqVPCjG69Up2clw9XS0zVDc+A=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=bD7KBRiS/ZzbTuJwei4m0YjYPe6LWuHRhOBHWeOXt99mPEqcwfGDYlRZlYLvddYHkNIOyjxR8Ofut5zrCjwe0nSqLi0rnHTki4n8xZwkUMm4qMQuL7gBthPAkKTaBJbDPcOtXPoYV4/tn2dgpqxgxWVepPdKgIKsjQkHLk/1EDU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=dRrG515o; arc=none smtp.client-ip=209.85.210.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="dRrG515o" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-82f896eb6faso171752b3a.3 for ; Thu, 16 Apr 2026 16:10:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1776381049; x=1776985849; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=9XumdmAM5k86iU84PyqR7i86FKgUtltq5DYpR2bGk2E=; b=dRrG515oZMzwI2pzmNx63Qpn13/SDeP6duvcPY15tCYOfEGk/9LhE+8bKRRpWIj5YW 3GKJ2Qibv6dJR96B2gr7g+xrovQ9gLo62mWrFwpkdOshSgXu3MbUWWUEBMDAoaiEHkFJ eparX9zkK5DZgk0MhaWh4JStTgUmlIxUVVQVGeXbd/6LttQ/lvV6AsbFu+0TTFZkFNf0 ZOh58nnJh7aU6ujEfXf07XVeb1Wvn7yMPYeVquTNn5FADnsfjZjOEs3S7+j8YvaHULUt SE4Otk8tpYyzleOC0X4JbEgY3GQAqR6uxl9jnWeX3eOPTHDAqXh9dtCJPhQ0jxylTqcZ g+pw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776381049; x=1776985849; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=9XumdmAM5k86iU84PyqR7i86FKgUtltq5DYpR2bGk2E=; b=bZY80IuZfZdT9UmuGLrDuOqoA60oVGjMmK0OIV79my5Z+Tnr8EE7v1jXHrvJS7IT/J TX5XNfnzOM01Y6LUOaBeVZSGSG8nbrp0OU/EWP9+kYf+OkhXrV2BSjJjLlMnpmSg2lrX iTtv/YHvX73LDm9I2aqndOu7wSrOQs5V6Wz/+Rx4TdX/AhH2yZNZbuauBbvICBA9LLh0 xb8T8XOhll32vqgvekDKGcFn89j+CB76e17nAAOQtMUoUBOuCbxLxEXJY4zNOXpSx8je K5tDLclvRPxi31HdrfSamWySjIDynTFHIAQ5HhCg1rrfIoQjceZrkZe7GrtmaiVBfEmU u6Aw== X-Forwarded-Encrypted: i=1; AFNElJ9gVwBqO79MjAtjoVGqjGCt+/S6FfIbHP8oNvIE5bnqYxQgu3hgWIXcAbTfDsFyHaJ0P0EHyvGzSwCGhc8=@vger.kernel.org X-Gm-Message-State: AOJu0Yy+alYnEqpY38bAlL/a7VYGPGrv22dwKbQ7Q8QaRiO2GtMEX+bm sM1Ar+cWo+nmDr4GgfHHi9UDW5JgPs51uBLYAGpPgDnM3N/4DMoegaJiivQJWVgdIiFMUfDl7fz J8WtM3Q== X-Received: from pfzz15.prod.google.com ([2002:a05:6a00:1ef:b0:82c:e899:f08d]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:3385:b0:82a:805a:7cc with SMTP id d2e1a72fcca58-82f8c7da23fmr229961b3a.4.1776381049416; Thu, 16 Apr 2026 16:10:49 -0700 (PDT) Reply-To: Sean Christopherson Date: Thu, 16 Apr 2026 16:10:38 -0700 In-Reply-To: <20260416231043.3402410-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260416231043.3402410-1-seanjc@google.com> X-Mailer: git-send-email 2.54.0.rc1.513.gad8abe7a5a-goog Message-ID: <20260416231043.3402410-2-seanjc@google.com> Subject: [PATCH v2 1/6] KVM: SVM: Fix page overflow in sev_dbg_crypt() for ENCRYPT path From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ashutosh Desai Content-Type: text/plain; charset="UTF-8" From: Ashutosh Desai In sev_dbg_crypt(), the per-iteration transfer length is bounded by the source page offset (PAGE_SIZE - s_off) but not by the destination page offset (PAGE_SIZE - d_off). When d_off > s_off, the encrypt path (__sev_dbg_encrypt_user) performs a read-modify-write using a single-page intermediate buffer (dst_tpage): 1. __sev_dbg_decrypt() expands the size to round_up(len + (d_off & 15), 16) before issuing the PSP command. If len + (d_off & 15) > PAGE_SIZE, the PSP writes beyond the end of the 4096-byte dst_tpage allocation. 2. The subsequent memcpy()/copy_from_user() into page_address(dst_tpage) + (d_off & 15) of 'len' bytes overflows by up to 15 bytes under the same condition. Trigger example: s_off = 0, d_off = 1, debug.len = PAGE_SIZE - the PSP is instructed to write round_up(4097, 16) = 4112 bytes to a 4096-byte buffer. Fix by also bounding len by (PAGE_SIZE - d_off), the same check that sev_send_update_data() already performs for its single-page guest region. ================================================================== BUG: KASAN: slab-use-after-free in sev_dbg_crypt+0x993/0xd10 [kvm_amd] Write of size 4095 at addr ff110062293bb009 by task sev_dbg_test/228214 CPU: 96 UID: 0 PID: 228214 Comm: sev_dbg_test Tainted: G U W 7.0.0-smp--5ce9b0c48211-dbg #156 PREEMPTLAZY Tainted: [U]=USER, [W]=WARN Hardware name: Google Astoria/astoria, BIOS 0.20250817.1-0 08/25/2025 Call Trace: dump_stack_lvl+0x54/0x70 print_report+0xbc/0x260 kasan_report+0xa2/0xd0 kasan_check_range+0x25f/0x2c0 __asan_memcpy+0x40/0x70 sev_dbg_crypt+0x993/0xd10 [kvm_amd] sev_mem_enc_ioctl+0x33c/0x450 [kvm_amd] kvm_vm_ioctl+0x65d/0x6d0 [kvm] __se_sys_ioctl+0xb2/0x100 do_syscall_64+0xe8/0x870 entry_SYSCALL_64_after_hwframe+0x4b/0x53 The buggy address belongs to the physical page: page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x7fe72b6a0 pfn:0x62293bb memcg:ff11000112827d82 flags: 0x1400000000000000(node=1|zone=1) raw: 1400000000000000 0000000000000000 dead000000000122 0000000000000000 raw: 00000007fe72b6a0 0000000000000000 00000001ffffffff ff11000112827d82 page dumped because: kasan: bad access detected Memory state around the buggy address: ff110062293bbf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff110062293bbf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >ff110062293bc000: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ^ ff110062293bc080: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ff110062293bc100: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ================================================================== Disabling lock debugging due to kernel taint Fixes: 24f41fb23a39 ("KVM: SVM: Add support for SEV DEBUG_DECRYPT command") Fixes: 7d1594f5d94b ("KVM: SVM: Add support for SEV DEBUG_ENCRYPT command") Cc: stable@vger.kernel.org Signed-off-by: Ashutosh Desai [sean: add sample KASAN splat, Fixes, and stable@] Signed-off-by: Sean Christopherson --- arch/x86/kvm/svm/sev.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index c2126b3c3072..b9d7bd868e0b 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -1396,6 +1396,7 @@ static int sev_dbg_crypt(struct kvm *kvm, struct kvm_sev_cmd *argp, bool dec) s_off = vaddr & ~PAGE_MASK; d_off = dst_vaddr & ~PAGE_MASK; len = min_t(size_t, (PAGE_SIZE - s_off), size); + len = min_t(size_t, len, PAGE_SIZE - d_off); if (dec) ret = __sev_dbg_decrypt_user(kvm, -- 2.54.0.rc1.513.gad8abe7a5a-goog