s390/bpf: Tolerate not converging code shrinking (1491b733) · Commits · 戴 / test

"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: ("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

arch/s390/net/bpf_jit_comp.c

+26 −1

Original line number	Diff line number	Diff line
		@@ -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
		*
		@@ -1503,7 +1521,14 @@ 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;

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