release/5.2.35/bpf-riscv-Limit-to-33-tail-calls.patch

From e2821f49351849abfd4f1247ebc71750bc6faad0 Mon Sep 17 00:00:00 2001
From: Paul Chaignon <paul.chaignon@orange.com>
Date: Mon, 9 Dec 2019 19:52:07 +0100
Subject: [PATCH] bpf, riscv: Limit to 33 tail calls
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commit 96bc4432f5ade1045521f3b247f516b1478166bd upstream.

All BPF JIT compilers except RISC-V's and MIPS' enforce a 33-tail calls
limit at runtime.  In addition, a test was recently added, in tailcalls2,
to check this limit.

This patch updates the tail call limit in RISC-V's JIT compiler to allow
33 tail calls.  I tested it using the above selftest on an emulated
RISCV64.

Fixes: 2353ecc6f91f ("bpf, riscv: add BPF JIT for RV64G")
Reported-by: Mahshid Khezri <khezri.mahshid@gmail.com>
Signed-off-by: Paul Chaignon <paul.chaignon@orange.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Björn Töpel <bjorn.topel@gmail.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/966fe384383bf23a0ee1efe8d7291c78a3fb832b.1575916815.git.paul.chaignon@gmail.com
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
index 426d5c33ea90..8783bb353224 100644
--- a/arch/riscv/net/bpf_jit_comp.c
+++ b/arch/riscv/net/bpf_jit_comp.c
@@ -631,14 +631,14 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
 		return -1;
 	emit(rv_bgeu(RV_REG_A2, RV_REG_T1, off >> 1), ctx);
 
-	/* if (--TCC < 0)
+	/* if (TCC-- < 0)
 	 *     goto out;
 	 */
 	emit(rv_addi(RV_REG_T1, tcc, -1), ctx);
 	off = (tc_ninsn - (ctx->ninsns - start_insn)) << 2;
 	if (is_13b_check(off, insn))
 		return -1;
-	emit(rv_blt(RV_REG_T1, RV_REG_ZERO, off >> 1), ctx);
+	emit(rv_blt(tcc, RV_REG_ZERO, off >> 1), ctx);
 
 	/* prog = array->ptrs[index];
 	 * if (!prog)
-- 
2.7.4