Re: [bpf-next v8 0/5] emit ENDBR/BTI instructions for indirect jump targets

["Alexis Lothoré" <alexis.lothore@bootlin.com>]

Hi Xu,

On Mon Mar 9, 2026 at 3:00 PM CET, Xu Kuohai wrote:
> On architectures with CFI protection enabled that require landing pad
> instructions at indirect jump targets, such as x86 with CET/IBT eanbled
> and arm64 with BTI enabled, kernel panics when an indirect jump lands on
> a target witout landing pad. Therefore, the JIT must emit landing pad
> instructions for indirect jump targets.
>
> The verifier already recognizes which instructions are indirect jump
> targets during the verification phase. So we can stores this information
> in env->insn_aux_data and pass it to the JIT as new parameter, so the JIT
> knows which instructions are indirect jump targets.
>
> During JIT, constants blinding is performed. It rewrites the private copy
> of instructions for the JITed program, but it does not adjust the global
> env->insn_aux_data array. As a result, after constants blinding, the
> instruction indexes used by JIT may no longer match the indexes in
> env->insn_aux_data, so the JIT can not lookup env->insn_aux_data directly.
>
> To avoid this mistach, and considering that all existing arch-specific JITs
> already implement constants blinding with largely duplicated code, move
> constants blinding from JIT to generic code, before copying instructions
> for each subprog.

Could you please add me in CC for any future revision ?

Thanks,

Alexis

-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com