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Thu, 23 Jan 2025 13:53:03 -0800 (PST) MIME-Version: 1.0 References: <20250123214342.4145818-1-andrii@kernel.org> In-Reply-To: <20250123214342.4145818-1-andrii@kernel.org> From: Suren Baghdasaryan Date: Thu, 23 Jan 2025 13:52:52 -0800 X-Gm-Features: AbW1kvYitEyfLCjZHD7-lTTvjs22unJX8NoVKvDf4fLvx82SDzv6eFu65vu0VC4 Message-ID: Subject: Re: [PATCH] mm,procfs: allow read-only remote mm access under CAP_PERFMON To: Andrii Nakryiko Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, brauner@kernel.org, viro@zeniv.linux.org.uk, 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, Jann Horn , Kees Cook Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: muc54otfq4qno1rd4ic9ym91nww6ncr7 X-Rspamd-Queue-Id: 1AAF640002 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1737669184-779714 X-HE-Meta: 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 i5joyKum uD4YeqUGyd51NLzViGXufuwUeXJDLGF0fz3TZ8dw7CHkX8yQRZrrNToQh4fdUfT1uwKca7Y3jDvLe67n8AJIM3jlH41DWl55O9is7/bWSRz1VSRpDUl9Prm1J+wEdaS94AoAO6zfeuwJ/rq9GFY1/LtlS4Na5UM7IKl76xFbyfOe0HWDGUydOXQfu7qa2Mq8yw0b5hPVNIC9/hSwNkUkj2klVQc+EJefs9245SbFh021LQ59sgWeLzjoOcJcvhsdKp+WKsWKIjAGyin8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000075, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jan 23, 2025 at 1:44=E2=80=AFPM Andrii Nakryiko = wrote: > > 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. CC'ing Jann and Kees. > > 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 =3D=3D 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 *tas= k, unsigned int mode) > mm =3D get_task_mm(task); > if (!mm) { > mm =3D ERR_PTR(-ESRCH); > - } else if (mm !=3D current->mm && !ptrace_may_access(task, mode))= { > + } else if (!can_access_mm(mm, task, mode)) { > mmput(mm); > mm =3D ERR_PTR(-EACCES); > } > -- > 2.43.5 >