From nobody Fri Mar 27 03:09:07 2026 Received: from mail-oi1-f202.google.com (mail-oi1-f202.google.com [209.85.167.202]) (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 4ACA63C6611 for ; Mon, 23 Mar 2026 17:54:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.202 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774288450; cv=none; b=sW+KRBVt5meNc1dPHE56DRqCLJCZpNTahR6gWYkjOs3MmcDdPf6Dds+8e3IETH+dW2SRcVFnGmzTiesgWMWx0grtoau6vEcBeK7VZO5wsRni2nIoYmhCE55VcHs0uhM1u/ZAYMeV2QM5pDkUPgVXeTEIs4VUGjmm0tItiQz3PTc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774288450; c=relaxed/simple; bh=IeY0RLDHZw+aV4EbbM8a2QRICo/GVGaL04vytj3zin0=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=aYamml1klmEYTWr204wJkb1MUz6m9h4sD1qxP8+EbipI1AzDCKpBtId2xdHsMASQWElSVDIV1gT2DMDCBQSV1hbYYRySH9PQJdx9NGgnMVY6EYKbOm4mul/XEdCcBNYOIO44rUPKBEz6mg/HAzqYpLMp7pc0BlnfimK9wAd0nEI= 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=fcFiFE6F; arc=none smtp.client-ip=209.85.167.202 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="fcFiFE6F" Received: by mail-oi1-f202.google.com with SMTP id 5614622812f47-467b2af6710so2853799b6e.2 for ; Mon, 23 Mar 2026 10:54:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1774288446; x=1774893246; 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=6mLJgPLWSuoj/P2MAtrzoRO0g8BMHCjkX0hvTYs5nb0=; b=fcFiFE6FCl3Zzyw+2twqkp0JK8bAiq6rxFUQ+kqSIP4zUnSjiy7Dy0MC+dU+xpiKNY boVaGOIRQ6+LiEKqddUXjxnRryWnwLqmYg4g1IRI4S5pDMfACjs/FJFthRFarXoeQMsW 2dHtrJVzmrpMiW4UHfzyc7B0oMEmRMPYH0Dgo0K1z4lUJCyMit5lzDoPSH+rv5hdyKRM mVYmNsbPk1mcgzFVNMlW6PJXj4YGdSELJSMCyKdwO2b9aWB/ZS3nkkqswkhBmiVHUu7L tLkowAubtLDxiVGso1O3aTn08DfRS1E5whIGWR3aYtadIx62/CTaCxGGnn5mwxeDILYk Niww== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774288446; x=1774893246; 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=6mLJgPLWSuoj/P2MAtrzoRO0g8BMHCjkX0hvTYs5nb0=; b=H/1DGI4RbEIKa7PMlFmePecus+xegoY2Lss9EqflLGWfpArHh/9K9nd6epHJ9HisXz nih9JapH8W55g2PSY2gP9hPrua/eEPhYD+XyBvo8JlHGSVaYyxQTwEhxV+HAeij3vkKv acA+DAsYPjwixVYvPxmhuJXAX4WoKhlJR/yeh3e0qP3qaJ483PE2YjuRPOh5O+BYKtvk U1S44vLTRJk/PCQkzDqD0zyaAn7paaNGlFnd1u8O0mnmdHrh7nWbYYduJ7afeu9rfPfk oRBqoPL7QE6kn5GYyEJg5g0ohYY/DBjXWdWNgnYM4Lv5NUNPi2LjwkHR/RkWQR5fog6g hcyg== X-Forwarded-Encrypted: i=1; AJvYcCUyka8RN9aFN52fpVsKGbsbB7D6E3xIMRfAaW9UjnbAXNDvgEAm/DLru3TyR+nmHpcZPcZwoNxRLzQoskQ=@vger.kernel.org X-Gm-Message-State: AOJu0YwZ+rQfN8w1VsuoqYzY+mZuU5lGC2o4Z0ipDxR+Z33p0PPDEz/k WPLDRVRqE3M6dC0kNhBYGJwEzkQh03d0AyF57jE5UMRtiHHlRzUhnnV/+aBRsoFVgEUB50JbP8f abP9E4A== X-Received: from ilbeb14.prod.google.com ([2002:a05:6e02:460e:b0:4f8:5be9:9dbe]) (user=avagin job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6820:612:b0:67d:ec7b:cc9d with SMTP id 006d021491bc7-67dec7bd049mr3051580eaf.18.1774288445933; Mon, 23 Mar 2026 10:54:05 -0700 (PDT) Date: Mon, 23 Mar 2026 17:53:39 +0000 In-Reply-To: <20260323175340.3361311-1-avagin@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260323175340.3361311-1-avagin@google.com> X-Mailer: git-send-email 2.53.0.983.g0bb29b3bc5-goog Message-ID: <20260323175340.3361311-4-avagin@google.com> Subject: [PATCH 3/4] mm: synchronize saved_auxv access with arg_lock From: Andrei Vagin To: Kees Cook , Andrew Morton Cc: Marek Szyprowski , Cyrill Gorcunov , Mike Rapoport , Alexander Mikhalitsyn , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, criu@lists.linux.dev, Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, 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 1cd7d87a0e79..dea868d058fa 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1791,6 +1791,7 @@ 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, val; =20 @@ -1831,6 +1832,7 @@ 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 4c863d17dfb4..b5496cec888e 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 62dde645f469..10351af5851b 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1255,7 +1255,6 @@ 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 2ac277aa078c..3880ce0d44f9 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1106,8 +1106,13 @@ 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 2.53.0.983.g0bb29b3bc5-goog