From e1fdd5e64fec0b7c08c2ca24beb610c66c6ff8f3 Mon Sep 17 00:00:00 2001 From: Puranjay Mohan Date: Tue, 12 Mar 2024 23:59:17 +0000 Subject: [PATCH] bpf, arm64: fix bug in BPF_LDX_MEMSX BugLink: https://bugs.launchpad.net/bugs/2065400 [ Upstream commit 114b5b3b4bde7358624437be2f12cde1b265224e ] A64_LDRSW() takes three registers: Xt, Xn, Xm as arguments and it loads and sign extends the value at address Xn + Xm into register Xt. Currently, the offset is being directly used in place of the tmp register which has the offset already loaded by the last emitted instruction. This will cause JIT failures. The easiest way to reproduce this is to test the following code through test_bpf module: { "BPF_LDX_MEMSX | BPF_W", .u.insns_int = { BPF_LD_IMM64(R1, 0x00000000deadbeefULL), BPF_LD_IMM64(R2, 0xffffffffdeadbeefULL), BPF_STX_MEM(BPF_DW, R10, R1, -7), BPF_LDX_MEMSX(BPF_W, R0, R10, -7), BPF_JMP_REG(BPF_JNE, R0, R2, 1), BPF_ALU64_IMM(BPF_MOV, R0, 0), BPF_EXIT_INSN(), }, INTERNAL, { }, { { 0, 0 } }, .stack_depth = 7, }, We need to use the offset as -7 to trigger this code path, there could be other valid ways to trigger this from proper BPF programs as well. This code is rejected by the JIT because -7 is passed to A64_LDRSW() but it expects a valid register (0 - 31). roott@pjy:~# modprobe test_bpf test_name="BPF_LDX_MEMSX | BPF_W" [11300.490371] test_bpf: test_bpf: set 'test_bpf' as the default test_suite. [11300.491750] test_bpf: #345 BPF_LDX_MEMSX | BPF_W [11300.493179] aarch64_insn_encode_register: unknown register encoding -7 [11300.494133] aarch64_insn_encode_register: unknown register encoding -7 [11300.495292] FAIL to select_runtime err=-524 [11300.496804] test_bpf: Summary: 0 PASSED, 1 FAILED, [0/0 JIT'ed] modprobe: ERROR: could not insert 'test_bpf': Invalid argument Applying this patch fixes the issue. root@pjy:~# modprobe test_bpf test_name="BPF_LDX_MEMSX | BPF_W" [ 292.837436] test_bpf: test_bpf: set 'test_bpf' as the default test_suite. [ 292.839416] test_bpf: #345 BPF_LDX_MEMSX | BPF_W jited:1 156 PASS [ 292.844794] test_bpf: Summary: 1 PASSED, 0 FAILED, [1/1 JIT'ed] Fixes: cc88f540da52 ("bpf, arm64: Support sign-extension load instructions") Signed-off-by: Puranjay Mohan Message-ID: <20240312235917.103626-1-puranjay12@gmail.com> Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin Signed-off-by: Manuel Diewald Signed-off-by: Roxana Nicolescu --- arch/arm64/net/bpf_jit_comp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index 8955da5c47cf77..582c4c2491edcc 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -1189,7 +1189,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, } else { emit_a64_mov_i(1, tmp, off, ctx); if (sign_extend) - emit(A64_LDRSW(dst, src_adj, off_adj), ctx); + emit(A64_LDRSW(dst, src, tmp), ctx); else emit(A64_LDR32(dst, src, tmp), ctx); }