From 738a96c4a8c36950803fdd27e7c30aca92dccefd Mon Sep 17 00:00:00 2001 From: Xu Kuohai Date: Sat, 1 Apr 2023 19:41:44 -0400 Subject: bpf, arm64: Fixed a BTI error on returning to patched function 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: : 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 Signed-off-by: Xu Kuohai Signed-off-by: Daniel Borkmann Tested-by: Florent Revest Acked-by: Florent Revest Link: https://lore.kernel.org/bpf/20230401234144.3719742-1-xukuohai@huaweicloud.com --- arch/arm64/net/bpf_jit.h | 4 ++++ arch/arm64/net/bpf_jit_comp.c | 3 ++- 2 files changed, 6 insertions(+), 1 deletion(-) (limited to 'arch') 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 */ -- cgit v1.2.3-70-g09d2