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| author | Alexander Duyck <alexanderduyck@fb.com> | 2023-07-13 19:49:31 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2023-07-19 01:28:19 +0300 |
| commit | a3f25d614bc73b45e8f02adc6769876dfd16ca84 (patch) | |
| tree | 708c5d0fa36a110c9f56b7698593f09a7ccb4d08 /arch | |
| parent | a8237cc87e3de1adb3f2f6a8056621e7e578cc00 (diff) | |
| download | linux-a3f25d614bc73b45e8f02adc6769876dfd16ca84.tar.xz | |
bpf, arm64: Fix BTI type used for freplace attached functions
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@ahduyck-xeon-server.home.arpa
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm64/net/bpf_jit_comp.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index 145b540ec34f..ec2174838f2a 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); |