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Message-ID: <20251227081033.240336-1-xukuohai@huaweicloud.com>
Date: Sat, 27 Dec 2025 16:10:33 +0800
From: Xu Kuohai <xukuohai@...weicloud.com>
To: bpf@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Eduard Zingerman <eddyz87@...il.com>,
Yonghong Song <yonghong.song@...ux.dev>,
Puranjay Mohan <puranjay@...nel.org>,
Anton Protopopov <a.s.protopopov@...il.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>
Subject: [PATCH bpf-next v3] bpf: arm64: Fix panic due to missing BTI at indirect jump targets
From: Xu Kuohai <xukuohai@...wei.com>
When BTI is enabled, the indirect jump selftest triggers BTI exception:
Internal error: Oops - BTI: 0000000036000003 [#1] SMP
...
Call trace:
bpf_prog_2e5f1c71c13ac3e0_big_jump_table+0x54/0xf8 (P)
bpf_prog_run_pin_on_cpu+0x140/0x464
bpf_prog_test_run_syscall+0x274/0x3ac
bpf_prog_test_run+0x224/0x2b0
__sys_bpf+0x4cc/0x5c8
__arm64_sys_bpf+0x7c/0x94
invoke_syscall+0x78/0x20c
el0_svc_common+0x11c/0x1c0
do_el0_svc+0x48/0x58
el0_svc+0x54/0x19c
el0t_64_sync_handler+0x84/0x12c
el0t_64_sync+0x198/0x19c
This happens because no BTI instruction is generated by the JIT for
indirect jump targets.
Fix it by emitting BTI instruction for every possible indirect jump
targets when BTI is enabled. The targets are identified by traversing
all instruction arrays of jump table type used by the BPF program,
since indirect jump targets can only be read from instruction arrays
of jump table type.
Fixes: f4a66cf1cb14 ("bpf: arm64: Add support for indirect jumps")
Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
---
v3:
- Get rid of unnecessary enum definition (Yonghong Song, Anton Protopopov)
v2: https://lore.kernel.org/bpf/20251223085447.139301-1-xukuohai@huaweicloud.com/
- Exclude instruction arrays not used for indirect jumps (Anton Protopopov)
v1: https://lore.kernel.org/bpf/20251127140318.3944249-1-xukuohai@huaweicloud.com/
---
arch/arm64/net/bpf_jit_comp.c | 20 +++++++++++
include/linux/bpf.h | 14 ++++++++
kernel/bpf/bpf_insn_array.c | 63 +++++++++++++++++++++++++++++++++++
kernel/bpf/verifier.c | 6 ++++
4 files changed, 103 insertions(+)
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 0c4d44bcfbf4..f08f0f9fa04e 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -78,6 +78,7 @@ static const int bpf2a64[] = {
struct jit_ctx {
const struct bpf_prog *prog;
+ unsigned long *indirect_targets;
int idx;
int epilogue_offset;
int *offset;
@@ -1199,6 +1200,11 @@ static int add_exception_handler(const struct bpf_insn *insn,
return 0;
}
+static bool is_indirect_target(int insn_off, unsigned long *targets_bitmap)
+{
+ return targets_bitmap && test_bit(insn_off, targets_bitmap);
+}
+
/* JITs an eBPF instruction.
* Returns:
* 0 - successfully JITed an 8-byte eBPF instruction.
@@ -1231,6 +1237,9 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
int ret;
bool sign_extend;
+ if (is_indirect_target(i, ctx->indirect_targets))
+ emit_bti(A64_BTI_J, ctx);
+
switch (code) {
/* dst = src */
case BPF_ALU | BPF_MOV | BPF_X:
@@ -2085,6 +2094,16 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
memset(&ctx, 0, sizeof(ctx));
ctx.prog = prog;
+ if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && bpf_prog_has_jump_table(prog)) {
+ ctx.indirect_targets = kvcalloc(BITS_TO_LONGS(prog->len), sizeof(unsigned long),
+ GFP_KERNEL);
+ if (ctx.indirect_targets == NULL) {
+ prog = orig_prog;
+ goto out_off;
+ }
+ bpf_prog_collect_indirect_targets(prog, ctx.indirect_targets);
+ }
+
ctx.offset = kvcalloc(prog->len + 1, sizeof(int), GFP_KERNEL);
if (ctx.offset == NULL) {
prog = orig_prog;
@@ -2248,6 +2267,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
prog->aux->priv_stack_ptr = NULL;
}
kvfree(ctx.offset);
+ kvfree(ctx.indirect_targets);
out_priv_stack:
kfree(jit_data);
prog->aux->jit_data = NULL;
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4e7d72dfbcd4..4a26346263bf 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3893,11 +3893,25 @@ void bpf_insn_array_adjust_after_remove(struct bpf_map *map, u32 off, u32 len);
#ifdef CONFIG_BPF_SYSCALL
void bpf_prog_update_insn_ptrs(struct bpf_prog *prog, u32 *offsets, void *image);
+void bpf_prog_collect_indirect_targets(const struct bpf_prog *prog, unsigned long *bitmap);
+void bpf_prog_mark_jump_table(struct bpf_map *map);
+bool bpf_prog_has_jump_table(const struct bpf_prog *prog);
#else
static inline void
bpf_prog_update_insn_ptrs(struct bpf_prog *prog, u32 *offsets, void *image)
{
}
+static inline void
+bpf_prog_collect_indirect_targets(const struct bpf_prog *prog, unsigned long *bitmap)
+{
+}
+static inline void bpf_prog_mark_jump_table(struct bpf_map *map)
+{
+}
+static inline bool bpf_prog_has_jump_table(const struct bpf_prog *prog)
+{
+ return false;
+}
#endif
static inline int bpf_map_check_op_flags(struct bpf_map *map, u64 flags, u64 allowed_flags)
diff --git a/kernel/bpf/bpf_insn_array.c b/kernel/bpf/bpf_insn_array.c
index c96630cb75bf..b9b43fdbe8e3 100644
--- a/kernel/bpf/bpf_insn_array.c
+++ b/kernel/bpf/bpf_insn_array.c
@@ -6,6 +6,7 @@
struct bpf_insn_array {
struct bpf_map map;
atomic_t used;
+ bool is_jump_table;
long *ips;
DECLARE_FLEX_ARRAY(struct bpf_insn_array_value, values);
};
@@ -302,3 +303,65 @@ void bpf_prog_update_insn_ptrs(struct bpf_prog *prog, u32 *offsets, void *image)
}
}
}
+
+void bpf_prog_mark_jump_table(struct bpf_map *map)
+{
+ struct bpf_insn_array *insn_array = cast_insn_array(map);
+
+ insn_array->is_jump_table = true;
+}
+
+static bool is_jump_table(const struct bpf_map *map)
+{
+ struct bpf_insn_array *insn_array;
+
+ if (!is_insn_array(map))
+ return false;
+
+ insn_array = cast_insn_array(map);
+ return insn_array->is_jump_table;
+}
+
+bool bpf_prog_has_jump_table(const struct bpf_prog *prog)
+{
+ int i;
+
+ for (i = 0; i < prog->aux->used_map_cnt; i++) {
+ if (is_jump_table(prog->aux->used_maps[i]))
+ return true;
+ }
+ return false;
+}
+
+/*
+ * This function collects possible indirect jump targets in a BPF program. Since indirect jump
+ * targets can only be read from indirect arrays used as jump table, it traverses all jump
+ * tables used by @prog. For each instruction found in the jump tables, it sets the corresponding
+ * bit in @bitmap.
+ */
+void bpf_prog_collect_indirect_targets(const struct bpf_prog *prog, unsigned long *bitmap)
+{
+ struct bpf_insn_array *insn_array;
+ struct bpf_map *map;
+ u32 xlated_off;
+ int i, j;
+
+ for (i = 0; i < prog->aux->used_map_cnt; i++) {
+ map = prog->aux->used_maps[i];
+ if (!is_jump_table(map))
+ continue;
+
+ insn_array = cast_insn_array(map);
+ for (j = 0; j < map->max_entries; j++) {
+ xlated_off = insn_array->values[j].xlated_off;
+ if (xlated_off == INSN_DELETED)
+ continue;
+ if (xlated_off < prog->aux->subprog_start)
+ continue;
+ xlated_off -= prog->aux->subprog_start;
+ if (xlated_off >= prog->len)
+ continue;
+ __set_bit(xlated_off, bitmap);
+ }
+ }
+}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2de1a736ef69..bc4a269ed06e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -20292,6 +20292,12 @@ static int check_indirect_jump(struct bpf_verifier_env *env, struct bpf_insn *in
return -EINVAL;
}
+ /*
+ * Explicitly mark this map as a jump table such that it can be
+ * distinguished later from other instruction arrays
+ */
+ bpf_prog_mark_jump_table(map);
+
for (i = 0; i < n - 1; i++) {
other_branch = push_stack(env, env->gotox_tmp_buf->items[i],
env->insn_idx, env->cur_state->speculative);
--
2.47.3
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