diff mbox series

[bpf] bpf, arm64: fix bug in BPF_LDX_MEMSX

Message ID 20240312235917.103626-1-puranjay12@gmail.com (mailing list archive)
State Accepted
Commit 114b5b3b4bde7358624437be2f12cde1b265224e
Delegated to: BPF
Headers show
Series [bpf] bpf, arm64: fix bug in BPF_LDX_MEMSX | expand

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Commit Message

Puranjay Mohan March 12, 2024, 11:59 p.m. UTC 
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 <puranjay12@gmail.com>
---
 arch/arm64/net/bpf_jit_comp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

patchwork-bot+netdevbpf@kernel.org March 20, 2024, 6 a.m. UTC | #1 
Hello:

This patch was applied to bpf/bpf.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Tue, 12 Mar 2024 23:59:17 +0000 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [bpf] bpf, arm64: fix bug in BPF_LDX_MEMSX
    https://git.kernel.org/bpf/bpf/c/114b5b3b4bde

You are awesome, thank you!
diff mbox series

Patch

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index c5b461dda438..48b19a233299 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -1256,7 +1256,7 @@  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);
 			}