From bdc18902ead81313dcdfecb922f44f44b63e756b Mon Sep 17 00:00:00 2001 From: Paul Burton Date: Fri, 15 Feb 2019 20:14:15 +0000 Subject: [PATCH] MIPS: eBPF: Always return sign extended 32b values The function prototype used to call JITed eBPF code (ie. the type of the struct bpf_prog bpf_func field) returns an unsigned int. The MIPS n64 ABI that MIPS64 kernels target defines that 32 bit integers should always be sign extended when passed in registers as either arguments or return values. This means that when returning any value which may not already be sign extended (ie. of type REG_64BIT or REG_32BIT_ZERO_EX) we need to perform that sign extension in order to comply with the n64 ABI. Without this we see strange looking test failures from test_bpf.ko, such as: test_bpf: #65 ALU64_MOV_X: dst = 4294967295 jited:1 ret -1 != -1 FAIL (1 times) Although the return value printed matches the expected value, this is only because printf is only examining the least significant 32 bits of the 64 bit register value we returned. The register holding the expected value is sign extended whilst the v0 register was set to a zero extended value by our JITed code, so when compared by a conditional branch instruction the values are not equal. We already handle this when the return value register is of type REG_32BIT_ZERO_EX, so simply extend this to also cover REG_64BIT. Signed-off-by: Paul Burton Fixes: b6bd53f9c4e8 ("MIPS: Add missing file for eBPF JIT.") Cc: stable@vger.kernel.org # v4.13+ Cc: linux-mips@vger.kernel.org Cc: Alexei Starovoitov Cc: Daniel Borkmann Cc: Martin KaFai Lau Cc: Song Liu Cc: Yonghong Song Cc: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: Jiong Wang --- arch/mips/net/ebpf_jit.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/mips/net/ebpf_jit.c b/arch/mips/net/ebpf_jit.c index b16710a..715415f 100644 --- a/arch/mips/net/ebpf_jit.c +++ b/arch/mips/net/ebpf_jit.c @@ -343,12 +343,15 @@ static int build_int_epilogue(struct jit_ctx *ctx, int dest_reg) const struct bpf_prog *prog = ctx->skf; int stack_adjust = ctx->stack_size; int store_offset = stack_adjust - 8; + enum reg_val_type td; int r0 = MIPS_R_V0; - if (dest_reg == MIPS_R_RA && - get_reg_val_type(ctx, prog->len, BPF_REG_0) == REG_32BIT_ZERO_EX) + if (dest_reg == MIPS_R_RA) { /* Don't let zero extended value escape. */ - emit_instr(ctx, sll, r0, r0, 0); + td = get_reg_val_type(ctx, prog->len, BPF_REG_0); + if (td == REG_64BIT || td == REG_32BIT_ZERO_EX) + emit_instr(ctx, sll, r0, r0, 0); + } if (ctx->flags & EBPF_SAVE_RA) { emit_instr(ctx, ld, MIPS_R_RA, store_offset, MIPS_R_SP); -- 2.7.4