From: Alexander Duyck alexanderduyck@fb.com
[ Upstream commit a3f25d614bc73b45e8f02adc6769876dfd16ca84 ]
When running an freplace attached bpf program on an arm64 system w were seeing the following issue: Unhandled 64-bit el1h sync exception on CPU47, ESR 0x0000000036000003 -- BTI
After a bit of work to track it down I determined that what appeared to be happening is that the 'bti c' at the start of the program was somehow being reached after a 'br' instruction. Further digging pointed me toward the fact that the function was attached via freplace. This in turn led me to build_plt which I believe is invoking the long jump which is triggering this error.
To resolve it we can replace the 'bti c' with 'bti jc' and add a comment explaining why this has to be modified as such.
Fixes: b2ad54e1533e ("bpf, arm64: Implement bpf_arch_text_poke() for arm64") Signed-off-by: Alexander Duyck alexanderduyck@fb.com Acked-by: Xu Kuohai xukuohai@huawei.com Link: https://lore.kernel.org/r/168926677665.316237.9953845318337455525.stgit@ahdu... Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/net/bpf_jit_comp.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index b26da8efa616e..0ce5f13eabb1b 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -322,7 +322,13 @@ static int build_prologue(struct jit_ctx *ctx, bool ebpf_from_cbpf) * */
- emit_bti(A64_BTI_C, ctx); + /* bpf function may be invoked by 3 instruction types: + * 1. bl, attached via freplace to bpf prog via short jump + * 2. br, attached via freplace to bpf prog via long jump + * 3. blr, working as a function pointer, used by emit_call. + * So BTI_JC should used here to support both br and blr. + */ + emit_bti(A64_BTI_JC, ctx);
emit(A64_MOV(1, A64_R(9), A64_LR), ctx); emit(A64_NOP, ctx);