lkml.org 
[lkml]   [2017]   [Dec]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: BPF: bug without effect in BPF_RSH case of adjust_scalar_min_max_vals()
On Mon, Dec 4, 2017 at 6:03 PM, Jann Horn <jannh@google.com> wrote:
> As far as I can tell, commit b03c9f9fdc37 ("bpf/verifier: track signed
> and unsigned min/max values") introduced the following effectless bug
> in the BPF_RSH case of adjust_scalar_min_max_vals() (unless that's
> intentional):
[...]
> =======================
> BPF_LD_MAP_FD(BPF_REG_ARG1, mapfd),
>
> BPF_MOV64_REG(BPF_REG_TMP, BPF_REG_FP),
> BPF_ALU64_IMM(BPF_ADD, BPF_REG_TMP, -4), // allocate 4 bytes stack
> BPF_MOV32_IMM(BPF_REG_ARG2, 1),
> BPF_STX_MEM(BPF_W, BPF_REG_TMP, BPF_REG_ARG2, 0),
> BPF_MOV64_REG(BPF_REG_ARG2, BPF_REG_TMP),
> BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 2),
> BPF_MOV64_REG(BPF_REG_0, 0), // prepare exit
> BPF_EXIT_INSN(), // exit
> BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_0, 0),
>
> BPF_ALU64_IMM(BPF_AND, BPF_REG_3, 0xf),
> BPF_MOV64_IMM(BPF_REG_1, -42),
> BPF_ALU64_REG(BPF_ADD, BPF_REG_1, BPF_REG_3),
> BPF_MOV64_IMM(BPF_REG_2, 2),
> BPF_ALU64_REG(BPF_RSH, BPF_REG_1, BPF_REG_2),
> BPF_EXIT_INSN()
> =======================

For using the eBPF bytecode in selftests:

Signed-off-by: Jann Horn <jannh@google.com>

\
 
 \ /
  Last update: 2017-12-04 21:27    [W:0.033 / U:9.516 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site