netdev - [PATCH bpf-next v3 4/7] bpf, arm64: Impelment bpf_arch_text

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Date:   Sun, 24 Apr 2022 11:40:25 -0400
From:   Xu Kuohai <xukuohai@...wei.com>
To:     <bpf@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        <hpa@...or.com>, Shuah Khan <shuah@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Daniel Kiss <daniel.kiss@....com>,
        Steven Price <steven.price@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Marc Zyngier <maz@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Mark Brown <broonie@...nel.org>,
        Delyan Kratunov <delyank@...com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: [PATCH bpf-next v3 4/7] bpf, arm64: Impelment bpf_arch_text_poke() for arm64

Impelment bpf_arch_text_poke() for arm64, so bpf trampoline code can use
it to replace nop with jump, or replace jump with nop.

Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
Acked-by: Song Liu <songliubraving@...com>
---
 arch/arm64/net/bpf_jit_comp.c | 63 +++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 8ab4035dea27..3f9bdfec54c4 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -9,6 +9,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/bpf.h>
+#include <linux/memory.h>
 #include <linux/filter.h>
 #include <linux/printk.h>
 #include <linux/slab.h>
@@ -18,6 +19,7 @@
 #include <asm/cacheflush.h>
 #include <asm/debug-monitors.h>
 #include <asm/insn.h>
+#include <asm/patching.h>
 #include <asm/set_memory.h>
 
 #include "bpf_jit.h"
@@ -1529,3 +1531,64 @@ void bpf_jit_free_exec(void *addr)
 {
 	return vfree(addr);
 }
+
+static int gen_branch_or_nop(enum aarch64_insn_branch_type type, void *ip,
+			     void *addr, u32 *insn)
+{
+	if (!addr)
+		*insn = aarch64_insn_gen_nop();
+	else
+		*insn = aarch64_insn_gen_branch_imm((unsigned long)ip,
+						    (unsigned long)addr,
+						    type);
+
+	return *insn != AARCH64_BREAK_FAULT ? 0 : -EFAULT;
+}
+
+int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
+		       void *old_addr, void *new_addr)
+{
+	int ret;
+	u32 old_insn;
+	u32 new_insn;
+	u32 replaced;
+	enum aarch64_insn_branch_type branch_type;
+
+	if (!is_bpf_text_address((long)ip))
+		/* Only poking bpf text is supported. Since kernel function
+		 * entry is set up by ftrace, we reply on ftrace to poke kernel
+		 * functions. For kernel funcitons, bpf_arch_text_poke() is only
+		 * called after a failed poke with ftrace. In this case, there
+		 * is probably something wrong with fentry, so there is nothing
+		 * we can do here. See register_fentry, unregister_fentry and
+		 * modify_fentry for details.
+		 */
+		return -EINVAL;
+
+	if (poke_type == BPF_MOD_CALL)
+		branch_type = AARCH64_INSN_BRANCH_LINK;
+	else
+		branch_type = AARCH64_INSN_BRANCH_NOLINK;
+
+	if (gen_branch_or_nop(branch_type, ip, old_addr, &old_insn) < 0)
+		return -EFAULT;
+
+	if (gen_branch_or_nop(branch_type, ip, new_addr, &new_insn) < 0)
+		return -EFAULT;
+
+	mutex_lock(&text_mutex);
+	if (aarch64_insn_read(ip, &replaced)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	if (replaced != old_insn) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	ret = aarch64_insn_patch_text_nosync((void *)ip, new_insn);
+out:
+	mutex_unlock(&text_mutex);
+	return ret;
+}
-- 
2.30.2