[PATCH bpf v9 5/8] 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/cmplwi for accurate comparision
in corresponding 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.h        | 6 ++++++
 arch/powerpc/net/bpf_jit_comp.c   | 2 +-
 arch/powerpc/net/bpf_jit_comp64.c | 8 ++++----
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
index 6632de9871dd..af510da12d8e 100644
--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -188,6 +188,12 @@ struct codegen_context {
 
 #define bpf_to_ppc(r)	(ctx->b2p[r])
 
+#ifdef CONFIG_PPC64
+#define PPC_RAW_CMPLLI(a, i)    PPC_RAW_CMPLDI(a, i)
+#else
+#define PPC_RAW_CMPLLI(a, i)    PPC_RAW_CMPLWI(a, i)
+#endif
+
 #ifdef CONFIG_PPC32
 #define BPF_FIXUP_LEN	3 /* Three instructions => 12 bytes */
 #else
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index e36efc09e133..1c274df2b4f7 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_CMPLLI(_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