From: Xu Kuohai <xukuohai@xxxxxxxxxx>
When BPF_TRAMP_F_CALL_ORIG is set, bpf trampoline uses BLR to jump
back to the instruction next to call site to call the patched function.
For BTI-enabled kernel, the instruction next to call site is usually
PACIASP, in this case, it's safe to jump back with BLR. But when
the call site is not followed by a PACIASP or bti, a BTI exception
is triggered.
Here is a fault log:
Unhandled 64-bit el1h sync exception on CPU0, ESR 0x0000000034000002 -- BTI
CPU: 0 PID: 263 Comm: test_progs Tainted: GF
Hardware name: linux,dummy-virt (DT)
pstate: 40400805 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=-c)
pc : bpf_fentry_test1+0xc/0x30
lr : bpf_trampoline_6442573892_0+0x48/0x1000
sp : ffff80000c0c3a50
x29: ffff80000c0c3a90 x28: ffff0000c2e6c080 x27: 0000000000000000
x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000050
x23: 0000000000000000 x22: 0000ffffcfd2a7f0 x21: 000000000000000a
x20: 0000ffffcfd2a7f0 x19: 0000000000000000 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 0000ffffcfd2a7f0
x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000000 x10: ffff80000914f5e4 x9 : ffff8000082a1528
x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0101010101010101
x5 : 0000000000000000 x4 : 00000000fffffff2 x3 : 0000000000000001
x2 : ffff8001f4b82000 x1 : 0000000000000000 x0 : 0000000000000001
Kernel panic - not syncing: Unhandled exception
CPU: 0 PID: 263 Comm: test_progs Tainted: GF
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace+0xec/0x144
show_stack+0x24/0x7c
dump_stack_lvl+0x8c/0xb8
dump_stack+0x18/0x34
panic+0x1cc/0x3ec
__el0_error_handler_common+0x0/0x130
el1h_64_sync_handler+0x60/0xd0
el1h_64_sync+0x78/0x7c
bpf_fentry_test1+0xc/0x30
bpf_fentry_test1+0xc/0x30
bpf_prog_test_run_tracing+0xdc/0x2a0
__sys_bpf+0x438/0x22a0
__arm64_sys_bpf+0x30/0x54
invoke_syscall+0x78/0x110
el0_svc_common.constprop.0+0x6c/0x1d0
do_el0_svc+0x38/0xe0
el0_svc+0x30/0xd0
el0t_64_sync_handler+0x1ac/0x1b0
el0t_64_sync+0x1a0/0x1a4
Kernel Offset: disabled
CPU features: 0x0000,00034c24,f994fdab
Memory Limit: none
And the instruction next to call site of bpf_fentry_test1 is ADD,
not PACIASP:
<bpf_fentry_test1>:
bti c
nop
nop
add w0, w0, #0x1
paciasp
For bpf prog, jit always puts a PACIASP after call site for BTI-enabled
kernel, so there is no problem.
To fix it, replace BLR with RET to bypass the branch target check.
Fixes: efc9909fdce0 ("bpf, arm64: Add bpf trampoline for arm64")
Reported-by: Florent Revest <revest@xxxxxxxxxxxx>
Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
---
arch/arm64/net/bpf_jit.h | 4 ++++
arch/arm64/net/bpf_jit_comp.c | 3 ++-
2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/net/bpf_jit.h b/arch/arm64/net/bpf_jit.h
index a6acb94ea3d6..c2edadb8ec6a 100644
--- a/arch/arm64/net/bpf_jit.h
+++ b/arch/arm64/net/bpf_jit.h
@@ -281,4 +281,8 @@
/* DMB */
#define A64_DMB_ISH aarch64_insn_gen_dmb(AARCH64_INSN_MB_ISH)
+/* ADR */
+#define A64_ADR(Rd, offset) \
+ aarch64_insn_gen_adr(0, offset, Rd, AARCH64_INSN_ADR_TYPE_ADR)
+
#endif /* _BPF_JIT_H */
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 62f805f427b7..b26da8efa616 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -1900,7 +1900,8 @@ static int prepare_trampoline(struct jit_ctx *ctx, struct bpf_tramp_image *im,
restore_args(ctx, args_off, nargs);
/* call original func */
emit(A64_LDR64I(A64_R(10), A64_SP, retaddr_off), ctx);
- emit(A64_BLR(A64_R(10)), ctx);
+ emit(A64_ADR(A64_LR, AARCH64_INSN_SIZE * 2), ctx);
+ emit(A64_RET(A64_R(10)), ctx);
/* store return value */
emit(A64_STR64I(A64_R(0), A64_SP, retval_off), ctx);
/* reserve a nop for bpf_tramp_image_put */
--
2.30.2
