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Commit 0a8a3e5b authored by Joel Fernandes's avatar Joel Fernandes
Browse files

BACKPORT: Add support for BPF_FUNC_probe_read_str 



Downstream kernel is missing support for this. It is needed by I/O
readahead project to read strings from kernel memory on Pixel v4.9. Add
support for the same.

Bug: 135210418

Change-Id: I37895b395d3fd2637f1d69e111c4a6e2b8c0327a
Signed-off-by: default avatarJoel Fernandes <joelaf@google.com>
parent b8f2f4b8

kernel/trace/bpf_trace.c

+31 −0
Original line number Diff line number Diff line
@@ -81,6 +81,35 @@ static const struct bpf_func_proto bpf_probe_read_proto = { 
	.arg3_type	= ARG_ANYTHING,

};



BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size, const void *, unsafe_ptr)

{

	int ret;



	/*

	 * The strncpy_from_unsafe() call will likely not fill the entire

	 * buffer, but that's okay in this circumstance as we're probing

	 * arbitrary memory anyway similar to bpf_probe_read() and might

	 * as well probe the stack. Thus, memory is explicitly cleared

	 * only in error case, so that improper users ignoring return

	 * code altogether don't copy garbage; otherwise length of string

	 * is returned that can be used for bpf_perf_event_output() et al.

	 */

	ret = strncpy_from_unsafe(dst, unsafe_ptr, size);

	if (unlikely(ret < 0))

		memset(dst, 0, size);



	return ret;

}



static const struct bpf_func_proto bpf_probe_read_str_proto = {

	.func           = bpf_probe_read_str,

	.gpl_only       = true,

	.ret_type       = RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_RAW_STACK,

	.arg2_type	= ARG_CONST_STACK_SIZE,

	.arg3_type	= ARG_ANYTHING,

};



BPF_CALL_3(bpf_probe_write_user, void *, unsafe_ptr, const void *, src,

	   u32, size)

{
@@ -434,6 +463,8 @@ 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_str:

		return &bpf_probe_read_str_proto;

	case BPF_FUNC_ktime_get_ns:

		return &bpf_ktime_get_ns_proto;

	case BPF_FUNC_tail_call: