From: Ilya Leoshkevich <iii@linux.ibm.com>
To: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>
Cc: bpf@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Ilya Leoshkevich <iii@linux.ibm.com>
Subject: [PATCH 4/5] s390/bpf: tolerate not converging code shrinking
Date: Fri, 17 Jul 2020 18:53:25 +0200 [thread overview]
Message-ID: <20200717165326.6786-5-iii@linux.ibm.com> (raw)
In-Reply-To: <20200717165326.6786-1-iii@linux.ibm.com>
"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>
---
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 625ebe32b2d1..e68854ab27ae 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -490,6 +490,24 @@ 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
*
@@ -1610,7 +1628,14 @@ 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;
--
2.25.4
next prev parent reply other threads:[~2020-07-17 16:56 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-17 16:53 [PATCH 0/5] s390/bpf: fix lib/test_bpf.c failures Ilya Leoshkevich
2020-07-17 16:53 ` [PATCH 1/5] selftests: bpf: test_kmod.sh: fix running out of srctree Ilya Leoshkevich
2020-07-17 16:53 ` [PATCH 2/5] s390/bpf: fix sign extension in branch_ku Ilya Leoshkevich
2020-07-17 22:23 ` Seth Forshee
2020-07-17 16:53 ` [PATCH 3/5] s390/bpf: use brcl for jumping to exit_ip if necessary Ilya Leoshkevich
2020-07-17 16:53 ` Ilya Leoshkevich [this message]
2020-07-17 16:53 ` [PATCH 5/5] s390/bpf: use bpf_skip() in bpf_jit_prologue() Ilya Leoshkevich
2020-07-21 18:17 ` [PATCH 0/5] s390/bpf: fix lib/test_bpf.c failures Alexei Starovoitov
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