Add a new BPF helper to read the VM of a process identified by PID.
Whilst PIDs are ambiguous without a namespace, many traditional
observability tools, like profilers and debuggers, accept a PID to
attach to a running process. The new helper proposed by this patch
is aimed at providing the capability of reading a remote process VM
to similar tools.
Signed-off-by: Gabriele N. Tornetta <phoenix1987@xxxxxxxxx>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 9 +++++++
kernel/bpf/helpers.c | 26 +++++++++++++++++++
kernel/trace/bpf_trace.c | 2 ++
scripts/bpf_doc.py | 1 +
tools/include/uapi/linux/bpf.h | 9 +++++++
.../selftests/bpf/prog_tests/test_lsm.c | 7 +++++
tools/testing/selftests/bpf/progs/lsm.c | 18 +++++++++++++
8 files changed, 73 insertions(+)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 6e947cd91152..96efa8912bbd 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2222,6 +2222,7 @@ extern const struct bpf_func_proto bpf_kallsyms_lookup_name_proto;
extern const struct bpf_func_proto bpf_find_vma_proto;
extern const struct bpf_func_proto bpf_loop_proto;
extern const struct bpf_func_proto bpf_strncmp_proto;
+extern const struct bpf_func_proto bpf_copy_from_user_remote_proto;
const struct bpf_func_proto *tracing_prog_func_proto(
enum bpf_func_id func_id, const struct bpf_prog *prog);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index b0383d371b9a..167ec1bc7248 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5018,6 +5018,14 @@ union bpf_attr {
*
* Return
* The number of arguments of the traced function.
+ *
+ * long bpf_copy_from_user_remote(void *dst, u32 size, pid_t pid, const void *user_ptr)
+ * Description
+ * Read *size* bytes from user space address *user_ptr* of the prodess
+ * *pid* and store the data in *dst*. This is essentially a wrapper of
+ * **access_process_vm**\ ().
+ * Return
+ * The number of bytes read on success, or a negative error in case of failure.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5206,6 +5214,7 @@ union bpf_attr {
FN(get_func_arg), \
FN(get_func_ret), \
FN(get_func_arg_cnt), \
+ FN(copy_from_user_remote), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 01cfdf40c838..c055eec77466 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -16,6 +16,7 @@
#include <linux/pid_namespace.h>
#include <linux/proc_ns.h>
#include <linux/security.h>
+#include <linux/mm.h>
#include "../../lib/kstrtox.h"
@@ -671,6 +672,31 @@ const struct bpf_func_proto bpf_copy_from_user_proto = {
.arg3_type = ARG_ANYTHING,
};
+BPF_CALL_4(bpf_copy_from_user_remote, void *, dst, u32, size,
+ pid_t, pid, const void __user *, user_ptr)
+{
+ struct task_struct *task;
+
+ if (unlikely(size == 0))
+ return 0;
+
+ task = find_get_task_by_vpid(pid);
+ if (!task)
+ return -ESRCH;
+
+ return access_process_vm(task, (unsigned long)user_ptr, dst, size, 0);
+}
+
+const struct bpf_func_proto bpf_copy_from_user_remote_proto = {
+ .func = bpf_copy_from_user_remote,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_UNINIT_MEM,
+ .arg2_type = ARG_CONST_SIZE_OR_ZERO,
+ .arg3_type = ARG_ANYTHING,
+ .arg4_type = ARG_ANYTHING,
+};
+
BPF_CALL_2(bpf_per_cpu_ptr, const void *, ptr, u32, cpu)
{
if (cpu >= nr_cpu_ids)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 21aa30644219..b30cd5e6d703 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1257,6 +1257,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_find_vma_proto;
case BPF_FUNC_trace_vprintk:
return bpf_get_trace_vprintk_proto();
+ case BPF_FUNC_copy_from_user_remote:
+ return prog->aux->sleepable ? &bpf_copy_from_user_remote_proto : NULL;
default:
return bpf_base_func_proto(func_id);
}
diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
index a6403ddf5de7..bd092f1692e2 100755
--- a/scripts/bpf_doc.py
+++ b/scripts/bpf_doc.py
@@ -614,6 +614,7 @@ class PrinterHelpers(Printer):
'const struct sk_buff': 'const struct __sk_buff',
'struct sk_msg_buff': 'struct sk_msg_md',
'struct xdp_buff': 'struct xdp_md',
+ "pid_t": "int",
}
# Helpers overloaded for different context types.
overloaded_helpers = [
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index b0383d371b9a..167ec1bc7248 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5018,6 +5018,14 @@ union bpf_attr {
*
* Return
* The number of arguments of the traced function.
+ *
+ * long bpf_copy_from_user_remote(void *dst, u32 size, pid_t pid, const void *user_ptr)
+ * Description
+ * Read *size* bytes from user space address *user_ptr* of the prodess
+ * *pid* and store the data in *dst*. This is essentially a wrapper of
+ * **access_process_vm**\ ().
+ * Return
+ * The number of bytes read on success, or a negative error in case of failure.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5206,6 +5214,7 @@ union bpf_attr {
FN(get_func_arg), \
FN(get_func_ret), \
FN(get_func_arg_cnt), \
+ FN(copy_from_user_remote), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/tools/testing/selftests/bpf/prog_tests/test_lsm.c b/tools/testing/selftests/bpf/prog_tests/test_lsm.c
index 244c01125126..71014141c675 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_lsm.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_lsm.c
@@ -56,6 +56,7 @@ static int test_lsm(struct lsm *skel)
struct bpf_link *link;
int buf = 1234;
int err;
+ int fd;
err = lsm__attach(skel);
if (!ASSERT_OK(err, "attach"))
@@ -86,6 +87,12 @@ static int test_lsm(struct lsm *skel)
ASSERT_EQ(skel->bss->copy_test, 3, "copy_test");
+ fd = syscall(__NR_open, "/dev/null", syscall(__NR_getpid));
+ if (fd >= 0)
+ syscall(__NR_close, fd);
+
+ ASSERT_EQ(skel->bss->copy_remote_test, 1, "copy_remote_test");
+
lsm__detach(skel);
skel->bss->copy_test = 0;
diff --git a/tools/testing/selftests/bpf/progs/lsm.c b/tools/testing/selftests/bpf/progs/lsm.c
index 33694ef8acfa..469ff988b0e9 100644
--- a/tools/testing/selftests/bpf/progs/lsm.c
+++ b/tools/testing/selftests/bpf/progs/lsm.c
@@ -177,3 +177,21 @@ int BPF_PROG(test_sys_setdomainname, struct pt_regs *regs)
copy_test++;
return 0;
}
+
+int copy_remote_test = 0;
+
+SEC("fentry.s/__x64_sys_open")
+int BPF_PROG(test_sys_open, struct pt_regs *regs)
+{
+ void *ptr = (void *)PT_REGS_PARM1(regs);
+ pid_t pid = (pid_t)PT_REGS_PARM2(regs);
+ char path[4];
+ long ret;
+
+ ret = bpf_copy_from_user_remote(&path, sizeof(path), pid, ptr);
+
+ if (ret == sizeof(path) && !__builtin_memcmp("/dev", path, 4))
+ copy_remote_test++;
+
+ return 0;
+}
--
2.30.2
