[PATCH bpf-next v5 3/6] bpf: Remove is_valid_bpf_tramp_flags()

From: Xu Kuohai <xukuohai@huawei.com>
To: <bpf@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>, <netdev@vger.kernel.org>,
	<linux-kselftest@vger.kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Alexei Starovoitov <ast@kernel.org>,
	Zi Shen Lim <zlim.lnx@gmail.com>,
	Andrii Nakryiko <andrii@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@kernel.org>,
	"David S . Miller" <davem@davemloft.net>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	David Ahern <dsahern@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>, <x86@kernel.org>,
	<hpa@zytor.com>, Shuah Khan <shuah@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Pasha Tatashin <pasha.tatashin@soleen.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Daniel Kiss <daniel.kiss@arm.com>,
	Steven Price <steven.price@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	Peter Collingbourne <pcc@google.com>,
	Mark Brown <broonie@kernel.org>, Delyan Kratunov <delyank@fb.com>,
	Kumar Kartikeya Dwivedi <memxor@gmail.com>
Subject: [PATCH bpf-next v5 3/6] bpf: Remove is_valid_bpf_tramp_flags()
Date: Wed, 18 May 2022 09:16:35 -0400	[thread overview]
Message-ID: <20220518131638.3401509-4-xukuohai@huawei.com> (raw)
In-Reply-To: <20220518131638.3401509-1-xukuohai@huawei.com>

BPF_TRAM_F_XXX flags are not used by user code and are almost constant
at compile time, so run time validation is a bit overkill. Remove
is_valid_bpf_tramp_flags() and add some usage comments.

Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Acked-by: Song Liu <songliubraving@fb.com>
---
 arch/x86/net/bpf_jit_comp.c | 20 --------------------
 kernel/bpf/bpf_struct_ops.c |  3 +++
 kernel/bpf/trampoline.c     |  3 +++
 3 files changed, 6 insertions(+), 20 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index a2b6d197c226..7698ef3b4821 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1922,23 +1922,6 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog,
 	return 0;
 }
 
-static bool is_valid_bpf_tramp_flags(unsigned int flags)
-{
-	if ((flags & BPF_TRAMP_F_RESTORE_REGS) &&
-	    (flags & BPF_TRAMP_F_SKIP_FRAME))
-		return false;
-
-	/*
-	 * BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,
-	 * and it must be used alone.
-	 */
-	if ((flags & BPF_TRAMP_F_RET_FENTRY_RET) &&
-	    (flags & ~BPF_TRAMP_F_RET_FENTRY_RET))
-		return false;
-
-	return true;
-}
-
 /* Example:
  * __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev);
  * its 'struct btf_func_model' will be nr_args=2
@@ -2017,9 +2000,6 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
 	if (nr_args > 6)
 		return -ENOTSUPP;
 
-	if (!is_valid_bpf_tramp_flags(flags))
-		return -EINVAL;
-
 	/* Generated trampoline stack layout:
 	 *
 	 * RBP + 8         [ return address  ]
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index d9a3c9207240..0572cc5aeb28 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -341,6 +341,9 @@ int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks,
 
 	tlinks[BPF_TRAMP_FENTRY].links[0] = link;
 	tlinks[BPF_TRAMP_FENTRY].nr_links = 1;
+	/* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,
+	 * and it must be used alone.
+	 */
 	flags = model->ret_size > 0 ? BPF_TRAMP_F_RET_FENTRY_RET : 0;
 	return arch_prepare_bpf_trampoline(NULL, image, image_end,
 					   model, flags, tlinks, NULL);
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 93c7675f0c9e..bd3f2e673874 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -358,6 +358,9 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
 
 	if (tlinks[BPF_TRAMP_FEXIT].nr_links ||
 	    tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links)
+		/* NOTE: BPF_TRAMP_F_RESTORE_REGS and BPF_TRAMP_F_SKIP_FRAME
+		 * should not be set together.
+		 */
 		flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
 
 	if (ip_arg)
-- 
2.30.2

