korg/linux
0
0
Fork 0
mirror of https://mirrors.bfsu.edu.cn/git/linux.git synced 2024-11-24 20:54:10 +08:00
Code Issues Packages Projects Releases Wiki Activity

s390/bpf: Emit a barrier for BPF_FETCH instructions

Browse Source 
BPF_ATOMIC_OP() macro documentation states that "BPF_ADD | BPF_FETCH"
should be the same as atomic_fetch_add(), which is currently not the
case on s390x: the serialization instruction "bcr 14,0" is missing.
This applies to "and", "or" and "xor" variants too.

s390x is allowed to reorder stores with subsequent fetches from
different addresses, so code relying on BPF_FETCH acting as a barrier,
for example:

  stw [%r0], 1
  afadd [%r1], %r2
  ldxw %r3, [%r4]

may be broken. Fix it by emitting "bcr 14,0".

Note that a separate serialization instruction is not needed for
BPF_XCHG and BPF_CMPXCHG, because COMPARE AND SWAP performs
serialization itself.

Fixes: ba3b86b9ce ("s390/bpf: Implement new atomic ops")
Reported-by: Puranjay Mohan <puranjay12@gmail.com>
Closes: https://lore.kernel.org/bpf/mb61p34qvq3wf.fsf@kernel.org/
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20240507000557.12048-1-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Ilya Leoshkevich 2024-05-07 02:02:49 +02:00 committed by Alexei Starovoitov
parent 55302bc1ca
commit 68378982f0
1 changed files with 6 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
arch/s390/net/bpf_jit_comp.c
View File

@ -1427,8 +1427,12 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
EMIT6_DISP_LH(0xeb000000, is32 ? (op32) : (op64), \ EMIT6_DISP_LH(0xeb000000, is32 ? (op32) : (op64), \
(insn->imm & BPF_FETCH) ? src_reg : REG_W0, \ (insn->imm & BPF_FETCH) ? src_reg : REG_W0, \
src_reg, dst_reg, off); \ src_reg, dst_reg, off); \
if (is32 && (insn->imm & BPF_FETCH)) \ if (insn->imm & BPF_FETCH) { \
EMIT_ZERO(src_reg); \ /* bcr 14,0 - see atomic_fetch_{add,and,or,xor}() */ \
_EMIT2(0x07e0); \
if (is32) \
EMIT_ZERO(src_reg); \
} \
} while (0) } while (0)
case BPF_ADD: case BPF_ADD:
case BPF_ADD | BPF_FETCH: case BPF_ADD | BPF_FETCH: