Messages in this thread | | | Date | Sat, 15 Jul 2023 17:03:44 +0800 | Subject | Re: [PATCH bpf] bpf, arm64: Fix BTI type used for freplace attached functions | From | Xu Kuohai <> |
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On 7/14/2023 12:49 AM, Alexander Duyck wrote: > From: Alexander Duyck <alexanderduyck@fb.com> > > 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> > --- > 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 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);
LGTM. Thanks for the fixes.
Acked-by: Xu Kuohai <xukuohai@huawei.com>
> > emit(A64_MOV(1, A64_R(9), A64_LR), ctx); > emit(A64_NOP, ctx); > >
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