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From: Jiri Olsa <jolsa@redhat.com>
To: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>
Subject: [PATCH bpf-next 07/29] bpf, x64: Allow to use caller address from stack
Date: Thu, 18 Nov 2021 12:24:33 +0100	[thread overview]
Message-ID: <20211118112455.475349-8-jolsa@kernel.org> (raw)
In-Reply-To: <20211118112455.475349-1-jolsa@kernel.org>

Currently we call the original function by using the absolute address
given at the JIT generation. That's not usable when having trampoline
attached to multiple functions. In this case we need to take the
return address from the stack.

Adding support to retrieve the original function address from the stack
by adding new BPF_TRAMP_F_ORIG_STACK flag for arch_prepare_bpf_trampoline
function.

Basically we take the return address of the 'fentry' call:

   function + 0: call fentry    # stores 'function + 5' address on stack
   function + 5: ...

The 'function + 5' address will be used as the address for the
original function to call.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 arch/x86/net/bpf_jit_comp.c | 13 +++++++++----
 include/linux/bpf.h         |  5 +++++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 67e8ac9aaf0d..d87001073033 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -2035,10 +2035,15 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
 	if (flags & BPF_TRAMP_F_CALL_ORIG) {
 		restore_regs(m, &prog, nr_args, stack_size);
 
-		/* call original function */
-		if (emit_call(&prog, orig_call, prog)) {
-			ret = -EINVAL;
-			goto cleanup;
+		if (flags & BPF_TRAMP_F_ORIG_STACK) {
+			emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, 8);
+			EMIT2(0xff, 0xd0); /* call *rax */
+		} else {
+			/* call original function */
+			if (emit_call(&prog, orig_call, prog)) {
+				ret = -EINVAL;
+				goto cleanup;
+			}
 		}
 		/* remember return value in a stack for bpf prog to access */
 		emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8);
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cc7a0c36e7df..77c76e2fa9ff 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -594,6 +594,11 @@ struct btf_func_model {
 /* Return the return value of fentry prog. Only used by bpf_struct_ops. */
 #define BPF_TRAMP_F_RET_FENTRY_RET	BIT(4)
 
+/* Get original function from stack instead of from provided direct address.
+ * Makes sense for fexit programs only.
+ */
+#define BPF_TRAMP_F_ORIG_STACK		BIT(5)
+
 /* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
  * bytes on x86.  Pick a number to fit into BPF_IMAGE_SIZE / 2
  */
-- 
2.31.1


  parent reply	other threads:[~2021-11-18 11:26 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-18 11:24 [RFC bpf-next v5 00/29] bpf: Add batch support for attaching trampolines Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 01/29] ftrace: Use direct_ops hash in unregister_ftrace_direct Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 02/29] ftrace: Add cleanup to unregister_ftrace_direct_multi Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 03/29] ftrace: Add ftrace_set_filter_ips function Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 04/29] bpf: Factor bpf_check_attach_target function Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 05/29] bpf: Add bpf_check_attach_model function Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 06/29] bpf: Add bpf_arg/bpf_ret_value helpers for tracing programs Jiri Olsa
2021-11-24 21:43   ` Andrii Nakryiko
2021-11-25 16:14     ` Alexei Starovoitov
2021-11-28 18:07       ` Jiri Olsa
2021-11-28 18:06     ` Jiri Olsa
2021-12-01  7:13       ` Andrii Nakryiko
2021-12-01 17:37         ` Alexei Starovoitov
2021-12-01 17:59           ` Andrii Nakryiko
2021-12-01 20:36             ` Alexei Starovoitov
2021-12-01 21:16             ` Jiri Olsa
2021-11-18 11:24 ` Jiri Olsa [this message]
2021-11-19  4:14   ` [PATCH bpf-next 07/29] bpf, x64: Allow to use caller address from stack Alexei Starovoitov
2021-11-19 21:46     ` Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 08/29] bpf: Keep active attached trampoline in bpf_prog Jiri Olsa
2021-11-24 21:48   ` Andrii Nakryiko
2021-11-28 17:24     ` Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 09/29] bpf: Add support to load multi func tracing program Jiri Olsa
2021-11-19  4:11   ` Alexei Starovoitov
2021-11-22 20:15     ` Jiri Olsa
2021-11-24 21:51       ` Andrii Nakryiko
2021-11-28 17:41         ` Jiri Olsa
2021-12-01  7:17           ` Andrii Nakryiko
2021-12-01 21:20             ` Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 10/29] bpf: Add bpf_trampoline_id object Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 11/29] bpf: Add addr to " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 12/29] bpf: Add struct bpf_tramp_node layer Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 13/29] bpf: Add bpf_tramp_attach layer for trampoline attachment Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 14/29] bpf: Add support to store multiple ids in bpf_tramp_id object Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 15/29] bpf: Add support to store multiple addrs " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 16/29] bpf: Add bpf_tramp_id_single function Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 17/29] bpf: Resolve id in bpf_tramp_id_single Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 18/29] bpf: Add refcount_t to struct bpf_tramp_id Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 19/29] bpf: Add support to attach trampolines with multiple IDs Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 20/29] bpf: Add support for tracing multi link Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 21/29] libbpf: Add btf__find_by_glob_kind function Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 22/29] libbpf: Add support to link multi func tracing program Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 23/29] selftests/bpf: Add bpf_arg/bpf_ret_value test Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 24/29] selftests/bpf: Add fentry multi func test Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 25/29] selftests/bpf: Add fexit " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 26/29] selftests/bpf: Add fentry/fexit " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 27/29] selftests/bpf: Add mixed " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 28/29] selftests/bpf: Add ret_mod " Jiri Olsa
2021-11-18 11:24 ` [PATCH bpf-next 29/29] selftests/bpf: Add attach " Jiri Olsa

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