Messages in this thread | | | Date | Mon, 6 May 2019 23:47:51 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH RFC] bpf: Add support for reading user pointers |
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Hi Joel,
On Thu, 2 May 2019 16:49:58 -0400 "Joel Fernandes (Google)" <joel@joelfernandes.org> wrote:
> The eBPF based opensnoop tool fails to read the file path string passed > to the do_sys_open function. This is because it is a pointer to > userspace address and causes an -EFAULT when read with > probe_kernel_read. This is not an issue when running the tool on x86 but > is an issue on arm64. This patch adds a new bpf function call based > which calls the recently proposed probe_user_read function [1]. > Using this function call from opensnoop fixes the issue on arm64. > > [1] https://lore.kernel.org/patchwork/patch/1051588/
Anyway, this series is still out-of-tree. We have to push this or similar update into kernel at first. I can resend v7 on the latest -tip tree including this patch if you update the description.
Thank you,
> > Cc: Michal Gregorczyk <michalgr@live.com> > Cc: Adrian Ratiu <adrian.ratiu@collabora.com> > Cc: Mohammad Husain <russoue@gmail.com> > Cc: Qais Yousef <qais.yousef@arm.com> > Cc: Srinivas Ramana <sramana@codeaurora.org> > Cc: duyuchao <yuchao.du@unisoc.com> > Cc: Manjo Raja Rao <linux@manojrajarao.com> > Cc: Karim Yaghmour <karim.yaghmour@opersys.com> > Cc: Tamir Carmeli <carmeli.tamir@gmail.com> > Cc: Yonghong Song <yhs@fb.com> > Cc: Alexei Starovoitov <ast@kernel.org> > Cc: Brendan Gregg <brendan.d.gregg@gmail.com> > Cc: Masami Hiramatsu <mhiramat@kernel.org> > Cc: Peter Ziljstra <peterz@infradead.org> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Kees Cook <keescook@chromium.org> > Cc: kernel-team@android.com > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> > --- > include/uapi/linux/bpf.h | 7 ++++++- > kernel/trace/bpf_trace.c | 22 ++++++++++++++++++++++ > tools/include/uapi/linux/bpf.h | 7 ++++++- > 3 files changed, 34 insertions(+), 2 deletions(-) > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index e99e3e6f8b37..6fec701eaa46 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -539,6 +539,10 @@ union bpf_attr { > * @mode: operation mode (enum bpf_adj_room_mode) > * @flags: reserved for future use > * Return: 0 on success or negative error code > + * > + * int bpf_probe_read_user(void *dst, int size, void *src) > + * Read a userspace pointer safely. > + * Return: 0 on success or negative error > */ > #define __BPF_FUNC_MAPPER(FN) \ > FN(unspec), \ > @@ -591,7 +595,8 @@ union bpf_attr { > FN(get_socket_uid), \ > FN(set_hash), \ > FN(setsockopt), \ > - FN(skb_adjust_room), > + FN(skb_adjust_room), \ > + FN(probe_read_user), > > /* integer value in 'imm' field of BPF_CALL instruction selects which helper > * function eBPF program intends to call > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index dc498b605d5d..1e1a11d9faa8 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -81,6 +81,26 @@ static const struct bpf_func_proto bpf_probe_read_proto = { > .arg3_type = ARG_ANYTHING, > }; > > +BPF_CALL_3(bpf_probe_read_user, void *, dst, u32, size, const void *, unsafe_ptr) > +{ > + int ret; > + > + ret = probe_user_read(dst, unsafe_ptr, size); > + if (unlikely(ret < 0)) > + memset(dst, 0, size); > + > + return ret; > +} > + > +static const struct bpf_func_proto bpf_probe_read_user_proto = { > + .func = bpf_probe_read_user, > + .gpl_only = true, > + .ret_type = RET_INTEGER, > + .arg1_type = ARG_PTR_TO_UNINIT_MEM, > + .arg2_type = ARG_CONST_SIZE, > + .arg3_type = ARG_ANYTHING, > +}; > + > BPF_CALL_3(bpf_probe_write_user, void *, unsafe_ptr, const void *, src, > u32, size) > { > @@ -459,6 +479,8 @@ static const struct bpf_func_proto *tracing_func_proto(enum bpf_func_id func_id) > return &bpf_map_delete_elem_proto; > case BPF_FUNC_probe_read: > return &bpf_probe_read_proto; > + case BPF_FUNC_probe_read_user: > + return &bpf_probe_read_user_proto; > case BPF_FUNC_ktime_get_ns: > return &bpf_ktime_get_ns_proto; > case BPF_FUNC_tail_call: > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h > index e99e3e6f8b37..6fec701eaa46 100644 > --- a/tools/include/uapi/linux/bpf.h > +++ b/tools/include/uapi/linux/bpf.h > @@ -539,6 +539,10 @@ union bpf_attr { > * @mode: operation mode (enum bpf_adj_room_mode) > * @flags: reserved for future use > * Return: 0 on success or negative error code > + * > + * int bpf_probe_read_user(void *dst, int size, void *src) > + * Read a userspace pointer safely. > + * Return: 0 on success or negative error > */ > #define __BPF_FUNC_MAPPER(FN) \ > FN(unspec), \ > @@ -591,7 +595,8 @@ union bpf_attr { > FN(get_socket_uid), \ > FN(set_hash), \ > FN(setsockopt), \ > - FN(skb_adjust_room), > + FN(skb_adjust_room), \ > + FN(probe_read_user), > > /* integer value in 'imm' field of BPF_CALL instruction selects which helper > * function eBPF program intends to call > -- > 2.21.0.593.g511ec345e18-goog >
-- Masami Hiramatsu <mhiramat@kernel.org>
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