From nobody Fri Apr 3 08:01:28 2026 Received: from mail-oo1-f73.google.com (mail-oo1-f73.google.com [209.85.161.73]) (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 BC41D37105D for ; Tue, 17 Feb 2026 18:01:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.73 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771351278; cv=none; b=XgATeN3AMB3ZU00q2A+3XSfGUDfpuv+kLal9bNdaFZ60noWsTrdICo5dn6CVdvPLeYjlLWXB53Ablv6T6sTCGKBkpVhmJ2ivWpMVjjV2tD5fFukSX6192tPtFMAeMIL9/c4paiMvg/IF9ymxt/L85RiHpf16TBcWTH+9kL66OVI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771351278; c=relaxed/simple; bh=3Hi4Yw1wa5t6RwBOUReTRUch3U2jt68qYKe1b8CJ15E=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=EXR0yqgtKC+Max5T/gXOvoAql7FLqT4D0qgYJe5S1BBlCC1JfuhieFv69pIrusxYyv34I7XbszU7x2eCqrTS0qNiSZnlG7dqYrNJ6sVRqo9RAq8LV/f3vfwpS2bwOBVnoyJancd/GU9xzpYchs5CO92V5kByHwPex7cZ8TkvEMg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--avagin.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=G/RRn3WG; arc=none smtp.client-ip=209.85.161.73 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--avagin.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="G/RRn3WG" Received: by mail-oo1-f73.google.com with SMTP id 006d021491bc7-679943693c0so23505172eaf.3 for ; Tue, 17 Feb 2026 10:01:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1771351276; x=1771956076; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=sNWH6w2foYf8QmhTrAmxhB/CQUCC0ZNVw0ETpO4TRL8=; b=G/RRn3WGXChfjYl416ZnkaHqChV1tM+Q/kJknc/q27uWFs+Oc1lYwp9i3wpYU6PChl vDTLO+2TijMCnpoCXI6t8rufTpfhamTeHdIxDvJAAeeo84d1mbgGe4N4UsagYHbuTMN8 tzkNc8nkNAZV+0auIr8CvNF2JtC7xdw3X05PjGPflu6huYKXCb1mmFkEPTIdXePFkjUJ eOD/62ZRuL2FGttlqodSjtGvEMGvXPl5yfA6L+HTZwmioqLNtbva11Ice/gehxwpHrD4 wFayBbS3GUC/VS6klopHSvX9dHEjwXC7JZxTXh8IV8xbhyW5OgEqnxNL0xQXeIq4xw19 5w2w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1771351276; x=1771956076; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=sNWH6w2foYf8QmhTrAmxhB/CQUCC0ZNVw0ETpO4TRL8=; b=bQFih8FhySsFLHWEGSe57qdwMe+ubLyY0kOhKYzVRgY8KLMddPwJ1muwW77NLBFnD+ ziVA4uk/4JtNIMFnB4z72yVh1MMyTcMouFeHL4R1YlLYtJYx0RdZTtCuZq67kdkm5FkI iOMYLbbDWDYFiDPghgCX1wNEz8utbZYCN3y0FMDOT/tx9LPdGrBccbGdFnwmFt1hT9wb lKe6qkXc8IkODeiSEbCC4knzd1bup3om1gnp6XY1+t3Y5nseUBeTgDvb82UoBNsSG9lE xHYPoiV4uQZ5eX2mbUG02oIrTtRrUMLT2EkmkBDtzLbir+anSAEgQ9M6a7ABLoLKU1iy KxBA== X-Forwarded-Encrypted: i=1; AJvYcCUfKooT+txa//4y4s1U5bdTYgO9/SaOHAlup46T4+pe5Q4sEAA58/Hcs6ta/S5Z1eEzvSrYDwThXsWVsSI=@vger.kernel.org X-Gm-Message-State: AOJu0YyfJ0LSYnOQz8q03ycrsPhVpGli/ZNz1nn7yMJEOvTl+2IdN6Jr ovT+aLIrGgEF797ETHOntwt4k2Qi0A1Ro+pcLofxq96b+JMsSijEUQl0C7kMXzNMp+31NMhO5qa lM6aXfA== X-Received: from jabko13.prod.google.com ([2002:a05:6638:8f0d:b0:5ce:aa0c:6674]) (user=avagin job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6820:1622:b0:66e:e7e:6524 with SMTP id 006d021491bc7-677690aef69mr8034820eaf.58.1771351275445; Tue, 17 Feb 2026 10:01:15 -0800 (PST) Date: Tue, 17 Feb 2026 18:01:07 +0000 In-Reply-To: <20260217180108.1420024-1-avagin@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260217180108.1420024-1-avagin@google.com> X-Mailer: git-send-email 2.53.0.310.g728cabbaf7-goog Message-ID: <20260217180108.1420024-4-avagin@google.com> Subject: [PATCH 3/4] mm: synchronize saved_auxv access with arg_lock From: Andrei Vagin To: Kees Cook , Andrew Morton Cc: Cyrill Gorcunov , Mike Rapoport , Alexander Mikhalitsyn , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, criu@lists.linux.dev, Chen Ridong , Christian Brauner , David Hildenbrand , Eric Biederman , Lorenzo Stoakes , Michal Koutny , Andrei Vagin , Alexander Mikhalitsyn Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The mm->saved_auxv array stores the auxiliary vector, which can be modified via prctl(PR_SET_MM_AUXV) or prctl(PR_SET_MM_MAP). Previously, accesses to saved_auxv were not synchronized. This was a intentional trade-off, as the vector was only used to provide information to userspace via /proc/PID/auxv or prctl(PR_GET_AUXV), and consistency between the auxv values left to userspace. With the introduction of hardware capability (HWCAP) inheritance during execve, the kernel now relies on the contents of saved_auxv to configure the execution environment of new processes. An unsynchronized read during execve could result in a new process inheriting an inconsistent set of capabilities if the parent process updates its auxiliary vector concurrently. While it is still not strictly required to guarantee the consistency of auxv values on the kernel side, doing so is relatively straightforward. This change implements synchronization using arg_lock. Reviewed-by: Alexander Mikhalitsyn Reviewed-by: Cyrill Gorcunov Reviewed-by: Michal Koutn=C3=BD Signed-off-by: Andrei Vagin --- fs/exec.c | 2 ++ fs/proc/base.c | 12 +++++++++--- include/linux/mm_types.h | 1 - kernel/fork.c | 7 ++++++- kernel/sys.c | 29 ++++++++++++++--------------- 5 files changed, 31 insertions(+), 20 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 9c70776fca9e..8f5fba06aff8 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1801,6 +1801,7 @@ static void inherit_hwcap(struct linux_binprm *bprm) n =3D 1; #endif =20 + spin_lock(&mm->arg_lock); for (i =3D 0; n && i < AT_VECTOR_SIZE; i +=3D 2) { unsigned long type =3D mm->saved_auxv[i]; unsigned long val =3D mm->saved_auxv[i + 1]; @@ -1832,6 +1833,7 @@ static void inherit_hwcap(struct linux_binprm *bprm) n--; } done: + spin_unlock(&mm->arg_lock); mm_flags_set(MMF_USER_HWCAP, bprm->mm); } =20 diff --git a/fs/proc/base.c b/fs/proc/base.c index 4eec684baca9..09d887741268 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1083,14 +1083,20 @@ static ssize_t auxv_read(struct file *file, char __= user *buf, { struct mm_struct *mm =3D file->private_data; unsigned int nwords =3D 0; + unsigned long saved_auxv[AT_VECTOR_SIZE]; =20 if (!mm) return 0; + + spin_lock(&mm->arg_lock); + memcpy(saved_auxv, mm->saved_auxv, sizeof(saved_auxv)); + spin_unlock(&mm->arg_lock); + do { nwords +=3D 2; - } while (mm->saved_auxv[nwords - 2] !=3D 0); /* AT_NULL */ - return simple_read_from_buffer(buf, count, ppos, mm->saved_auxv, - nwords * sizeof(mm->saved_auxv[0])); + } while (saved_auxv[nwords - 2] !=3D 0); /* AT_NULL */ + return simple_read_from_buffer(buf, count, ppos, saved_auxv, + nwords * sizeof(saved_auxv[0])); } =20 static const struct file_operations proc_auxv_operations =3D { diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 2f3c6ad48c0a..d1a95b90e448 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1254,7 +1254,6 @@ struct mm_struct { unsigned long start_code, end_code, start_data, end_data; unsigned long start_brk, brk, start_stack; unsigned long arg_start, arg_end, env_start, env_end; - unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */ =20 #ifdef CONFIG_ARCH_HAS_ELF_CORE_EFLAGS diff --git a/kernel/fork.c b/kernel/fork.c index 4c92a2bc3cbb..e17e57e29b6a 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1105,8 +1105,13 @@ static struct mm_struct *mm_init(struct mm_struct *m= m, struct task_struct *p, __mm_flags_overwrite_word(mm, mmf_init_legacy_flags(flags)); mm->def_flags =3D current->mm->def_flags & VM_INIT_DEF_MASK; =20 - if (mm_flags_test(MMF_USER_HWCAP, current->mm)) + if (mm_flags_test(MMF_USER_HWCAP, current->mm)) { + spin_lock(¤t->mm->arg_lock); mm_flags_set(MMF_USER_HWCAP, mm); + memcpy(mm->saved_auxv, current->mm->saved_auxv, + sizeof(mm->saved_auxv)); + spin_unlock(¤t->mm->arg_lock); + } } else { __mm_flags_overwrite_word(mm, default_dump_filter); mm->def_flags =3D 0; diff --git a/kernel/sys.c b/kernel/sys.c index e4b0fa2f6845..c679b5797e73 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2147,20 +2147,11 @@ static int prctl_set_mm_map(int opt, const void __u= ser *addr, unsigned long data mm->arg_end =3D prctl_map.arg_end; mm->env_start =3D prctl_map.env_start; mm->env_end =3D prctl_map.env_end; - spin_unlock(&mm->arg_lock); - - /* - * Note this update of @saved_auxv is lockless thus - * if someone reads this member in procfs while we're - * updating -- it may get partly updated results. It's - * known and acceptable trade off: we leave it as is to - * not introduce additional locks here making the kernel - * more complex. - */ if (prctl_map.auxv_size) { - memcpy(mm->saved_auxv, user_auxv, sizeof(user_auxv)); mm_flags_set(MMF_USER_HWCAP, mm); + memcpy(mm->saved_auxv, user_auxv, sizeof(user_auxv)); } + spin_unlock(&mm->arg_lock); =20 mmap_read_unlock(mm); return 0; @@ -2190,10 +2181,10 @@ static int prctl_set_auxv(struct mm_struct *mm, uns= igned long addr, =20 BUILD_BUG_ON(sizeof(user_auxv) !=3D sizeof(mm->saved_auxv)); =20 - task_lock(current); - memcpy(mm->saved_auxv, user_auxv, len); + spin_lock(&mm->arg_lock); mm_flags_set(MMF_USER_HWCAP, mm); - task_unlock(current); + memcpy(mm->saved_auxv, user_auxv, len); + spin_unlock(&mm->arg_lock); =20 return 0; } @@ -2481,9 +2472,17 @@ static inline int prctl_get_mdwe(unsigned long arg2,= unsigned long arg3, static int prctl_get_auxv(void __user *addr, unsigned long len) { struct mm_struct *mm =3D current->mm; + unsigned long auxv[AT_VECTOR_SIZE]; unsigned long size =3D min_t(unsigned long, sizeof(mm->saved_auxv), len); =20 - if (size && copy_to_user(addr, mm->saved_auxv, size)) + if (!size) + return sizeof(mm->saved_auxv); + + spin_lock(&mm->arg_lock); + memcpy(auxv, mm->saved_auxv, size); + spin_unlock(&mm->arg_lock); + + if (copy_to_user(addr, auxv, size)) return -EFAULT; return sizeof(mm->saved_auxv); } --=20 2.53.0.310.g728cabbaf7-goog