Re: [syzbot] [bpf?] KMSAN: uninit-value in ieee802154_subif_start_xmit

[Eduard Zingerman]

On Mon, 2023-08-07 at 16:11 +0300, Eduard Zingerman wrote:
[...]
>   $ bpftool prog dump jited id <some-id>
>   bpf_prog_ebeed182d92b487f:
>      0: nopl    (%rax,%rax)
>      5: nop
>      7: pushq   %rbp
>      8: movq    %rsp, %rbp
>      b: subq    $8, %rsp
>     12: movl    $553656332, -8(%rbp)
>     19: movswq  %bp, %rdi            ; <---- Note movswq %bp !
>     1d: addq    $-8, %rdi
>     21: movl    $3, %esi
>     26: cmpq    %rdi, %rsi
>     29: jbe 0x2b
>     2b: callq   0xffffffffe11c484c
>     30: xorl    %eax, %eax
>     32: leave
>     33: retq
> 
> Note jit instruction #19 corresponding to BPF instruction #1, which
> loads truncated and sign-extended value of %rbp's first byte as an
> address of format string.

Correction: sign-extended value of %rbp's first *two* bytes,
disassembly with opcodes:

  19:	movswq	%bp, %rdi
    48 0f bf fd 

[...]