[PATCH bpf-next v3 4/7] bpf, arm64: Impelment bpf_arch_text_poke() for arm64

Xu Kuohai
2022-04-24T15:34:05Z

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@huawei.com>
Acked-by: Song Liu <songliubraving@fb.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