[PATCH bpf-next v2] add function metadata support
Menglong Dong
menglong8.dong at gmail.com
Fri Feb 28 05:01:16 PST 2025
On Fri, Feb 28, 2025 at 6:26 PM Peter Zijlstra <peterz at infradead.org> wrote:
>
> On Fri, Feb 28, 2025 at 05:53:07PM +0800, Menglong Dong wrote:
>
> > I tested it a little by enabling CFI_CLANG and the extra 5-bytes
> > padding. It works fine, as mostly CFI_CLANG use
> > CONFIG_FUNCTION_PADDING_BYTES to find the tags. I'll
> > do more testing on CFI_CLANG to make sure everything goes
> > well.
>
> I don't think you understand; please read:
>
> arch/x86/kernel/alternative.c:__apply_fineibt()
>
> and all the code involved with patching FineIBT. I think you'll find it
> very broken if you change anything here.
>
> Can you post an actual function preamble from a kernel with
> CONFIG_FINEIBT=y with your changes on?
>
> Ex.
>
> $ objdump -wdr build/kernel/futex/core.o
>
> Disassembly of section .text:
>
> 0000000000000000 <__cfi_futex_hash>:
> 0: b9 93 0c f9 ad mov $0xadf90c93,%ecx
>
> 0000000000000005 <.Ltmp0>:
> 5: 90 nop
> 6: 90 nop
> 7: 90 nop
> 8: 90 nop
> 9: 90 nop
> a: 90 nop
> b: 90 nop
> c: 90 nop
> d: 90 nop
> e: 90 nop
> f: 90 nop
>
> 0000000000000010 <futex_hash>:
> 10: f3 0f 1e fa endbr64
> 14: e8 00 00 00 00 call 19 <futex_hash+0x9> 15: R_X86_64_PLT32 __fentry__-0x4
> 19: 8b 47 10 mov 0x10(%rdi),%eax
>
>
> Any change to the layout here *WILL* break the FineIBT code.
>
>
> If you want to test, make sure your build has FINEIBT=y and boot on an
> Intel CPU that has CET-IBT (alderlake and later).
Yeah, I understand now. As I see the definition of CFI_PRE_PADDING, I
know that things is not as simple as I thought, as the layout can be different
with different config. I'll dig it deeper on this part.
Thanks a lot for clearing that up for me. I'll test the CFI_CLANG and
FINEIBT together with this function later.
Thanks!
Menglong Dong
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