[PATCH v7 5/7] powerpc64/bpf: fix compare instruction emitted for tailcall

[adubey@linux.ibm.com]

From: Abhishek Dubey <adubey@linux.ibm.com>

The tail_call_info field can contain either a scalar counter
value or a 64-bit pointer to the counter, using a 32-bit
compare (cmplwi) only checks the lower 32 bits, which can lead
to incorrect comparisions when location of counter is near 4GB
boundary. Use instruction cmpldi for accurate comparision in
all cases.

Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/bpf/20260517191450.85AE6C2BCB8@smtp.kernel.org/
Fixes: 2ed2d8f6fb38 ("powerpc64/bpf: Support tailcalls with subprogs")
Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>
---
 arch/powerpc/net/bpf_jit_comp.c   | 2 +-
 arch/powerpc/net/bpf_jit_comp64.c | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index ebee23d33396..b36b55f12a8b 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -763,7 +763,7 @@ static void bpf_trampoline_setup_tail_call_info(u32 *image, struct codegen_conte
 		 * Setting the tail_call_info in trampoline's frame
 		 * depending on if previous frame had value or reference.
 		 */
-		EMIT(PPC_RAW_CMPLWI(_R3, MAX_TAIL_CALL_CNT));
+		EMIT(PPC_RAW_CMPLDI(_R3, MAX_TAIL_CALL_CNT));
 		PPC_BCC_CONST_SHORT(COND_GT, 8);
 		EMIT(PPC_RAW_ADDI(_R3, _R4, -BPF_PPC_TAILCALL));
 
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index eaf816a07f14..086084abb184 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -276,7 +276,7 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
 		 */
 		EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_2), _R1, 0));
 		EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_2), -(BPF_PPC_TAILCALL)));
-		EMIT(PPC_RAW_CMPLWI(bpf_to_ppc(TMP_REG_1), MAX_TAIL_CALL_CNT));
+		EMIT(PPC_RAW_CMPLDI(bpf_to_ppc(TMP_REG_1), MAX_TAIL_CALL_CNT));
 		PPC_BCC_CONST_SHORT(COND_GT, 8);
 		EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_2),
 								-(BPF_PPC_TAILCALL)));
@@ -651,7 +651,7 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
 	PPC_BCC_SHORT(COND_GE, out);
 
 	EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), _R1, bpf_jit_stack_tailcallinfo_offset(ctx)));
-	EMIT(PPC_RAW_CMPLWI(bpf_to_ppc(TMP_REG_1), MAX_TAIL_CALL_CNT));
+	EMIT(PPC_RAW_CMPLDI(bpf_to_ppc(TMP_REG_1), MAX_TAIL_CALL_CNT));
 	PPC_BCC_CONST_SHORT(COND_LE, 8);
 
 	/* dereference TMP_REG_1 */
@@ -661,7 +661,7 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
 	 * if (tail_call_info == MAX_TAIL_CALL_CNT)
 	 *   goto out;
 	 */
-	EMIT(PPC_RAW_CMPLWI(bpf_to_ppc(TMP_REG_1), MAX_TAIL_CALL_CNT));
+	EMIT(PPC_RAW_CMPLDI(bpf_to_ppc(TMP_REG_1), MAX_TAIL_CALL_CNT));
 	PPC_BCC_SHORT(COND_EQ, out);
 
 	/*
@@ -696,7 +696,7 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
 	 * tail_call_info.
 	 */
 	EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_2), _R1, bpf_jit_stack_tailcallinfo_offset(ctx)));
-	EMIT(PPC_RAW_CMPLWI(bpf_to_ppc(TMP_REG_2), MAX_TAIL_CALL_CNT));
+	EMIT(PPC_RAW_CMPLDI(bpf_to_ppc(TMP_REG_2), MAX_TAIL_CALL_CNT));
 	PPC_BCC_CONST_SHORT(COND_GT, 8);
 
 	/* First get address of tail_call_info */
-- 
2.52.0