From patchwork Thu Jan 23 21:43:42 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrii Nakryiko X-Patchwork-Id: 13948647 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 920548BF8; Thu, 23 Jan 2025 21:44:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737668649; cv=none; b=kt6zFM0IPU1mWfvCqXNncZMrOPU2Zc1nFB1QJ0CNh/NBH0zEgzgYiR5WhTcycg5D1KAeLLwbl3JXaq7ot7mD78ddPQw3nucfl2Wd7gV5v2CGLuN3sjIAwBa8HtJKKTcgKGGgfwxkGVdpV1NZln3jywrbOdvKyIe2E99n4bnlaVo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737668649; c=relaxed/simple; bh=R85lw46lWbNKwIBjKcm0nPFbL7eV+3oJagH3JDMENic=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=BmOzlUL+nMs1z3CX5+CqVBCHaKTrNa5NnxmehW3TRs541HS/QvIkaPURBtylpc71IlpSY4HzBaKW9TgrfdJWultNGano/OE4IOnFAsKjt/YcMSjEfT9G1K1ukuBbaT/zLlsS9EKOkvhdMlAhn/4ipbZ+10X35NiGSf67tD/PKsU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YGRqBL/k; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="YGRqBL/k" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7964C4CED3; Thu, 23 Jan 2025 21:44:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1737668649; bh=R85lw46lWbNKwIBjKcm0nPFbL7eV+3oJagH3JDMENic=; h=From:To:Cc:Subject:Date:From; b=YGRqBL/k5NSeLv2lvBxmXoUTbvMhc5e4DucR0zIIXXpZFHcApqrD7CdjkV+WKfdaf p2RVk4P34gOSLzAF/ndbuuV96NKi4UGLY239QVETaMRmPUNn3U+Uv5dGzWCMbQ5s82 3Z9rPxzLgfzke5hOz6pEYBGcTH5Sl1bZdl/aV+o8gfDyHvcvt2UHD+OmVWd7DnVH+Q fsA4ZqaQd3a14N3G/FLqZOh3XpGZTvxnAi+rMwaGyyVP1Rs1bnghl44oBtyGXU1/N0 wi/KdZ3+ORlGxlaFejSGFmNzobtElNImr+HEhoXeIOdnzNp4QaqnmomxFK2mardbjO NDcTnul24Y0lQ== From: Andrii Nakryiko To: linux-mm@kvack.org, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, brauner@kernel.org, viro@zeniv.linux.org.uk Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, peterz@infradead.org, mingo@kernel.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, shakeel.butt@linux.dev, rppt@kernel.org, liam.howlett@oracle.com, surenb@google.com, Andrii Nakryiko Subject: [PATCH] mm,procfs: allow read-only remote mm access under CAP_PERFMON Date: Thu, 23 Jan 2025 13:43:42 -0800 Message-ID: <20250123214342.4145818-1-andrii@kernel.org> X-Mailer: git-send-email 2.43.5 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 It's very common for various tracing and profiling toolis to need to access /proc/PID/maps contents for stack symbolization needs to learn which shared libraries are mapped in memory, at which file offset, etc. Currently, access to /proc/PID/maps requires CAP_SYS_PTRACE (unless we are looking at data for our own process, which is a trivial case not too relevant for profilers use cases). Unfortunately, CAP_SYS_PTRACE implies way more than just ability to discover memory layout of another process: it allows to fully control arbitrary other processes. This is problematic from security POV for applications that only need read-only /proc/PID/maps (and other similar read-only data) access, and in large production settings CAP_SYS_PTRACE is frowned upon even for the system-wide profilers. On the other hand, it's already possible to access similar kind of information (and more) with just CAP_PERFMON capability. E.g., setting up PERF_RECORD_MMAP collection through perf_event_open() would give one similar information to what /proc/PID/maps provides. CAP_PERFMON, together with CAP_BPF, is already a very common combination for system-wide profiling and observability application. As such, it's reasonable and convenient to be able to access /proc/PID/maps with CAP_PERFMON capabilities instead of CAP_SYS_PTRACE. For procfs, these permissions are checked through common mm_access() helper, and so we augment that with cap_perfmon() check *only* if requested mode is PTRACE_MODE_READ. I.e., PTRACE_MODE_ATTACH wouldn't be permitted by CAP_PERFMON. Besides procfs itself, mm_access() is used by process_madvise() and process_vm_{readv,writev}() syscalls. The former one uses PTRACE_MODE_READ to avoid leaking ASLR metadata, and as such CAP_PERFMON seems like a meaningful allowable capability as well. process_vm_{readv,writev} currently assume PTRACE_MODE_ATTACH level of permissions (though for readv PTRACE_MODE_READ seems more reasonable, but that's outside the scope of this change), and as such won't be affected by this patch. Signed-off-by: Andrii Nakryiko --- kernel/fork.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index ded49f18cd95..c57cb3ad9931 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1547,6 +1547,15 @@ struct mm_struct *get_task_mm(struct task_struct *task) } EXPORT_SYMBOL_GPL(get_task_mm); +static bool can_access_mm(struct mm_struct *mm, struct task_struct *task, unsigned int mode) +{ + if (mm == current->mm) + return true; + if ((mode & PTRACE_MODE_READ) && perfmon_capable()) + return true; + return ptrace_may_access(task, mode); +} + struct mm_struct *mm_access(struct task_struct *task, unsigned int mode) { struct mm_struct *mm; @@ -1559,7 +1568,7 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode) mm = get_task_mm(task); if (!mm) { mm = ERR_PTR(-ESRCH); - } else if (mm != current->mm && !ptrace_may_access(task, mode)) { + } else if (!can_access_mm(mm, task, mode)) { mmput(mm); mm = ERR_PTR(-EACCES); }