| From 03ac76adbe9267250fa91d9ca0b1eb89b0c1987c Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Fri, 17 Jul 2020 18:53:25 +0200 |
| Subject: s390/bpf: Tolerate not converging code shrinking |
| |
| From: Ilya Leoshkevich <iii@linux.ibm.com> |
| |
| [ Upstream commit 1491b73311a15bb5beeab5d30e03bff761ef6c18 ] |
| |
| "BPF_MAXINSNS: Maximum possible literals" unnecessarily falls back to |
| the interpreter because of failing sanity check in bpf_set_addr. The |
| problem is that there are a lot of branches that can be shrunk, and |
| doing so opens up the possibility to shrink even more. This process |
| does not converge after 3 passes, causing code offsets to change during |
| the codegen pass, which must never happen. |
| |
| Fix by inserting nops during codegen pass in order to preserve code |
| offets. |
| |
| Fixes: 4e9b4a6883dd ("s390/bpf: Use relative long branches") |
| Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> |
| Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
| Link: https://lore.kernel.org/bpf/20200717165326.6786-5-iii@linux.ibm.com |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| arch/s390/net/bpf_jit_comp.c | 27 ++++++++++++++++++++++++++- |
| 1 file changed, 26 insertions(+), 1 deletion(-) |
| |
| diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c |
| index 650b89eb693e6..95809599ebffd 100644 |
| --- a/arch/s390/net/bpf_jit_comp.c |
| +++ b/arch/s390/net/bpf_jit_comp.c |
| @@ -489,6 +489,24 @@ static void save_restore_regs(struct bpf_jit *jit, int op, u32 stack_depth) |
| } while (re <= last); |
| } |
| |
| +static void bpf_skip(struct bpf_jit *jit, int size) |
| +{ |
| + if (size >= 6 && !is_valid_rel(size)) { |
| + /* brcl 0xf,size */ |
| + EMIT6_PCREL_RIL(0xc0f4000000, size); |
| + size -= 6; |
| + } else if (size >= 4 && is_valid_rel(size)) { |
| + /* brc 0xf,size */ |
| + EMIT4_PCREL(0xa7f40000, size); |
| + size -= 4; |
| + } |
| + while (size >= 2) { |
| + /* bcr 0,%0 */ |
| + _EMIT2(0x0700); |
| + size -= 2; |
| + } |
| +} |
| + |
| /* |
| * Emit function prologue |
| * |
| @@ -1502,7 +1520,14 @@ static bool bpf_is_new_addr_sane(struct bpf_jit *jit, int i) |
| */ |
| static int bpf_set_addr(struct bpf_jit *jit, int i) |
| { |
| - if (!bpf_is_new_addr_sane(jit, i)) |
| + int delta; |
| + |
| + if (is_codegen_pass(jit)) { |
| + delta = jit->prg - jit->addrs[i]; |
| + if (delta < 0) |
| + bpf_skip(jit, -delta); |
| + } |
| + if (WARN_ON_ONCE(!bpf_is_new_addr_sane(jit, i))) |
| return -1; |
| jit->addrs[i] = jit->prg; |
| return 0; |
| -- |
| 2.25.1 |
| |