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From:   Puranjay Mohan <puranjay12@gmail.com>
To:     Alexei Starovoitov <ast@kernel.org>,
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Cc:     puranjay12@gmail.com
Subject: [PATCH bpf-next 4/6] bpf, powerpc32: Always zero extend for LDX
Date:   Tue, 12 Sep 2023 22:46:52 +0000
Message-Id: <20230912224654.6556-5-puranjay12@gmail.com>
In-Reply-To: <20230912224654.6556-1-puranjay12@gmail.com>
References: <20230912224654.6556-1-puranjay12@gmail.com>
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The JITs should not depend on the verifier for zero extending the upper
32 bits of the destination register when loading a byte, half-word, or
word.

A following patch will make the verifier stop patching zext instructions
after LDX.

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
---
 arch/powerpc/net/bpf_jit_comp32.c | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
index 7f91ea064c08..0a952a2cfaac 100644
--- a/arch/powerpc/net/bpf_jit_comp32.c
+++ b/arch/powerpc/net/bpf_jit_comp32.c
@@ -936,14 +936,13 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 				PPC_BCC_SHORT(COND_GT, (ctx->idx + 4) * 4);
 				EMIT(PPC_RAW_LI(dst_reg, 0));
 				/*
-				 * For BPF_DW case, "li reg_h,0" would be needed when
-				 * !fp->aux->verifier_zext. Emit NOP otherwise.
+				 * For BPF_DW case, "li reg_h,0" would be needed emit NOP otherwise.
 				 *
 				 * Note that "li reg_h,0" is emitted for BPF_B/H/W case,
 				 * if necessary. So, jump there insted of emitting an
 				 * additional "li reg_h,0" instruction.
 				 */
-				if (size == BPF_DW && !fp->aux->verifier_zext)
+				if (size == BPF_DW)
 					EMIT(PPC_RAW_LI(dst_reg_h, 0));
 				else
 					EMIT(PPC_RAW_NOP());
@@ -974,7 +973,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 				break;
 			}
 
-			if (size != BPF_DW && !fp->aux->verifier_zext)
+			if (size != BPF_DW)
 				EMIT(PPC_RAW_LI(dst_reg_h, 0));
 
 			if (BPF_MODE(code) == BPF_PROBE_MEM) {
@@ -982,20 +981,12 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 				int jmp_off = 4;
 
 				/*
-				 * In case of BPF_DW, two lwz instructions are emitted, one
-				 * for higher 32-bit and another for lower 32-bit. So, set
-				 * ex->insn to the first of the two and jump over both
-				 * instructions in fixup.
-				 *
-				 * Similarly, with !verifier_zext, two instructions are
-				 * emitted for BPF_B/H/W case. So, set ex->insn to the
-				 * instruction that could fault and skip over both
-				 * instructions.
+				 * Two instructions are emitted for LDX.
+				 * So, set ex->insn to the instruction that could fault and skip
+				 * over both instructions.
 				 */
-				if (size == BPF_DW || !fp->aux->verifier_zext) {
-					insn_idx -= 1;
-					jmp_off += 4;
-				}
+				insn_idx -= 1;
+				jmp_off += 4;
 
 				ret = bpf_add_extable_entry(fp, image, pass, ctx, insn_idx,
 							    jmp_off, dst_reg);
-- 
2.39.2