From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 923B153C3DF for ; Thu, 17 Sep 2026 16:40:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789663204; cv=none; b=tQspDSzaLUnUR/C83Lq+w7M4TytcsipexivSVm2a+0XrnrpiLIbHAJo6MEmbF2TVXauVX5vwacriwDZnNPHGmUgqWoUrUy5ui2PkacgvukpVVO6jJviAMUpw+8lYZWl1+RAx/QvZ9VzShpQquU6z7JF/5Dqe4yDBPTAugBZKZHI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789663204; c=relaxed/simple; bh=NK9QnmZYrfIfeFV82sEqPuCkYqEOXkcd8NmXUVmNY8s=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=FPqExVooA/vnGwUlVrwh5UNpG8y9JNVTVS/s37DEG6jvdjYRR7RsT0bUOeHR8IW3LjxcMeW1MpD1D0vHTMV9uERibPQS1pJc2VlH4+tsJCfoelBbi+iG6g84eMjjpqsA8yJzfSYIq71J6VSpfm6+BQk9BFU9yprQhS7SEt1/3bM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=XlU3qVnD; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="XlU3qVnD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EADB21F000FF; Thu, 17 Sep 2026 16:40:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789663203; bh=jPxHrfVOLylIirkgqbg7KSy0PccglWbqqVOtbpA2HoA=; h=From:To:Cc:Subject:Date:Reply-To; b=XlU3qVnDEaVLsD23745HG2nAqmGqP8RuJ0IqXzXqVleTXFzhsVvsmVlG3ERmTy7Ws DOKnHn3UER+izzRBdkBEzNlUqEcH3OSJzS/T90Uu3YyT4pyCo4SM68vszF435JZIMh z7y19K/siP5TDldE2lTlmSblzSMX6xkdlEKLHgxw= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-93164: uprobes/x86: Move optimized uprobe from nop5 to nop10 Date: Thu, 17 Sep 2026 17:17:21 +0100 Message-ID: <2026091758-CVE-2026-93164-e070@gregkh> X-Mailer: git-send-email 2.55.0 Reply-To: , Precedence: bulk X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=5561; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=4M8IVsbktVmgwD+nrnm+6tRR7TVFBbwTghbuHu3wV7Y=; b=owGbwMvMwCRo6H6F97bub03G02pJDFlrBK55lx3btmtH9TIfLv8I553PfZQc2gLmWWxf8a9wk +qx0u9/OmJZGASZGGTFFFm+bOM5ur/ikKKXoe1pmDmsTCBDGLg4BWAi+b4M8/2Xxx6/UZO62WJn y5P3TybsejbP2IthwcaEezESx+819JS4lFzgjP4rerh4DwA= X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: uprobes/x86: Move optimized uprobe from nop5 to nop10 Andrii reported an issue with optimized uprobes [1] that can clobber redzone area with call instruction storing return address on stack where user code may keep temporary data without adjusting rsp. Fixing this by moving the optimized uprobes on top of 10-bytes nop instruction, so we can squeeze another instruction to escape the redzone area before doing the call, like: lea -0x80(%rsp), %rsp call tramp Note the lea instruction is used to adjust the rsp register without changing the flags. We use nop10 and following transformation to optimized instructions above and back as suggested by Peterz [2]. Optimize path (int3_update_optimize): 1) Initial state after set_swbp() installed the uprobe: cc 2e 0f 1f 84 00 00 00 00 00 From offset 0 this is INT3 followed by the tail of the original 10-byte NOP. After a previous unoptimization bytes 5..9 may still contain the old call instruction, which remains valid for threads already there. 2) Rewrite the LEA tail and call displacement: cc [8d 64 24 80 e8 d0 d1 d2 d3] From offset 0 this traps on the uprobe INT3. Bytes 1..9 are not executable entry points while byte 0 is trapped. 3) Publish the first LEA byte: [48] 8d 64 24 80 e8 d0 d1 d2 d3 From offset 0 this is: lea -0x80(%rsp), %rsp call Unoptimize path (int3_update_unoptimize): 1) Initial optimized state: 48 8d 64 24 80 e8 d0 d1 d2 d3 Same as 3) above. 2) Trap new entries before restoring the NOP bytes: [cc] 8d 64 24 80 e8 d0 d1 d2 d3 From offset 0 this traps. A thread that had already executed the LEA can still reach the intact CALL at offset 5. 3) Restore bytes 1..4 of the original NOP while keeping byte 0 trapped and byte 5 as CALL. cc [2e 0f 1f 84] e8 d0 d1 d2 d3 From offset 0 this still traps. Offset 5 is still the CALL for any thread that was already past the first LEA byte. 4) Publish the first byte of the original NOP: [66] 2e 0f 1f 84 e8 d0 d1 d2 d3 From offset 0 this is the restored 10-byte NOP; the CALL opcode and displacement are now only NOP operands. Offset 5 still decodes as CALL for a thread that was already there. Tthere is only a single target uprobe-trampoline for the given nop10 instruction address, so the CALL instruction will not be changed across unoptimization/optimization cycles. Therefore, any task that is preempted at the CALL instruction is guaranteed to observe that CALL and not anything else. Note as explained in [2] we need to use following nop10: PF1 PF2 ESC NOPL MOD SIB DISP32 NOP10: 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 -- cs nopw 0x00000000(%rax,%rax,1) which means we need to allow 0x2e prefix which maps to INAT_PFX_CS attribute in is_prefix_bad function. Also changing the uprobe syscall error when called out of uprobe trampoline to -EPROTO, so we are able to detect the fixed kernel. The optimized uprobe performance stays the same: uprobe-nop : 3.129 ± 0.013M/s uprobe-push : 3.045 ± 0.006M/s uprobe-ret : 1.095 ± 0.004M/s --> uprobe-nop10 : 7.170 ± 0.020M/s uretprobe-nop : 2.143 ± 0.021M/s uretprobe-push : 2.090 ± 0.000M/s uretprobe-ret : 0.942 ± 0.000M/s --> uretprobe-nop10: 3.381 ± 0.003M/s usdt-nop : 3.245 ± 0.004M/s --> usdt-nop10 : 7.256 ± 0.023M/s [1] https://lore.kernel.org/bpf/20260509003146.976844-1-andrii@kernel.org/ [2] https://lore.kernel.org/bpf/20260518104306.GU3102624@noisy.programming.kicks-ass.net/#t The Linux kernel CVE team has assigned CVE-2026-93164 to this issue. Affected and fixed versions =========================== Issue introduced in 6.18 with commit ba2bfc97b4629b10bd8d02b36e04f3932a04cac4 and fixed in 7.2.6 with commit 1b3fecd09910040668b752f3377d7218ca5c59ac Issue introduced in 6.18 with commit ba2bfc97b4629b10bd8d02b36e04f3932a04cac4 and fixed in 7.3-rc1 with commit 554ba38456dad8053a1a80afe6ae6da9eff745cc Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2026-93164 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: arch/x86/kernel/uprobes.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/1b3fecd09910040668b752f3377d7218ca5c59ac https://git.kernel.org/stable/c/554ba38456dad8053a1a80afe6ae6da9eff745cc