powerpc/bpf: fix JIT code size calculation of bpf trampoline

JIRA: https://issues.redhat.com/browse/RHEL-24555

commit 59ba025
Author: Hari Bathini <hbathini@linux.ibm.com>
Date:   Tue Apr 22 13:56:09 2025 +0530

    powerpc/bpf: fix JIT code size calculation of bpf trampoline

    arch_bpf_trampoline_size() provides JIT size of the BPF trampoline
    before the buffer for JIT'ing it is allocated. The total number of
    instructions emitted for BPF trampoline JIT code depends on where
    the final image is located. So, the size arrived at with the dummy
    pass in arch_bpf_trampoline_size() can vary from the actual size
    needed in  arch_prepare_bpf_trampoline().  When the instructions
    accounted in  arch_bpf_trampoline_size() is less than the number of
    instructions emitted during the actual JIT compile of the trampoline,
    the below warning is produced:

      WARNING: CPU: 8 PID: 204190 at arch/powerpc/net/bpf_jit_comp.c:981 __arch_prepare_bpf_trampoline.isra.0+0xd2c/0xdcc

    which is:

      /* Make sure the trampoline generation logic doesn't overflow */
      if (image && WARN_ON_ONCE(&image[ctx->idx] >
                            (u32 *)rw_image_end - BPF_INSN_SAFETY)) {

    So, during the dummy pass, instead of providing some arbitrary image
    location, account for maximum possible instructions if and when there
    is a dependency with image location for JIT'ing.

    Fixes: d243b62 ("powerpc64/bpf: Add support for bpf trampolines")
    Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
    Closes: https://lore.kernel.org/all/6168bfc8-659f-4b5a-a6fb-90a916dde3b3@linux.ibm.com/
    Cc: stable@vger.kernel.org # v6.13+
    Acked-by: Naveen N Rao (AMD) <naveen@kernel.org>
    Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
    Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
    Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
    Link: https://patch.msgid.link/20250422082609.949301-1-hbathini@linux.ibm.com

Signed-off-by: Viktor Malik <vmalik@redhat.com>

Author: viktormalik

arch/powerpc/net/bpf_jit.h

@@ -51,19 +51,32 @@
 		EMIT(PPC_INST_BRANCH_COND | (((cond) & 0x3ff) << 16) | (offset & 0xfffc));					\
 	} while (0)
 
-/* Sign-extended 32-bit immediate load */
+/*
+ * Sign-extended 32-bit immediate load
+ *
+ * If this is a dummy pass (!image), account for
+ * maximum possible instructions.
+ */
 #define PPC_LI32(d, i)		do {					      \
+	if (!image)							      \
+		ctx->idx += 2;						      \
+	else {								      \
 		if ((int)(uintptr_t)(i) >= -32768 &&			      \
 				(int)(uintptr_t)(i) < 32768)		      \
 			EMIT(PPC_RAW_LI(d, i));				      \
 		else {							      \
 			EMIT(PPC_RAW_LIS(d, IMM_H(i)));			      \
 			if (IMM_L(i))					      \
 				EMIT(PPC_RAW_ORI(d, d, IMM_L(i)));	      \
-		} } while(0)
+		}							      \
+	} } while (0)
 
 #ifdef CONFIG_PPC64
+/* If dummy pass (!image), account for maximum possible instructions */
 #define PPC_LI64(d, i)		do {					      \
+	if (!image)							      \
+		ctx->idx += 5;						      \
+	else {								      \
 		if ((long)(i) >= -2147483648 &&				      \
 				(long)(i) < 2147483648)			      \
 			PPC_LI32(d, i);					      \
@@ -84,7 +97,8 @@
 			if ((uintptr_t)(i) & 0x000000000000ffffULL)	      \
 				EMIT(PPC_RAW_ORI(d, d, (uintptr_t)(i) &       \
 							0xffff));             \
-		} } while (0)
+		}							      \
+	} } while (0)
 #define PPC_LI_ADDR	PPC_LI64
 
 #ifndef CONFIG_PPC_KERNEL_PCREL

arch/powerpc/net/bpf_jit_comp.c

@@ -504,10 +504,11 @@ static int invoke_bpf_prog(u32 *image, u32 *ro_image, struct codegen_context *ct
 	EMIT(PPC_RAW_ADDI(_R3, _R1, regs_off));
 	if (!p->jited)
 		PPC_LI_ADDR(_R4, (unsigned long)p->insnsi);
-	if (!create_branch(&branch_insn, (u32 *)&ro_image[ctx->idx], (unsigned long)p->bpf_func,
-			   BRANCH_SET_LINK)) {
-		if (image)
-			image[ctx->idx] = ppc_inst_val(branch_insn);
+	/* Account for max possible instructions during dummy pass for size calculation */
+	if (image && !create_branch(&branch_insn, (u32 *)&ro_image[ctx->idx],
+				    (unsigned long)p->bpf_func,
+				    BRANCH_SET_LINK)) {
+		image[ctx->idx] = ppc_inst_val(branch_insn);
 		ctx->idx++;
 	} else {
 		EMIT(PPC_RAW_LL(_R12, _R25, offsetof(struct bpf_prog, bpf_func)));
@@ -889,7 +890,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
 			bpf_trampoline_restore_tail_call_cnt(image, ctx, func_frame_offset, r4_off);
 
 		/* Reserve space to patch branch instruction to skip fexit progs */
-		im->ip_after_call = &((u32 *)ro_image)[ctx->idx];
+		if (ro_image) /* image is NULL for dummy pass */
+			im->ip_after_call = &((u32 *)ro_image)[ctx->idx];
 		EMIT(PPC_RAW_NOP());
 	}
 
@@ -912,7 +914,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
 		}
 
 	if (flags & BPF_TRAMP_F_CALL_ORIG) {
-		im->ip_epilogue = &((u32 *)ro_image)[ctx->idx];
+		if (ro_image) /* image is NULL for dummy pass */
+			im->ip_epilogue = &((u32 *)ro_image)[ctx->idx];
 		PPC_LI_ADDR(_R3, im);
 		ret = bpf_jit_emit_func_call_rel(image, ro_image, ctx,
 						 (unsigned long)__bpf_tramp_exit);
@@ -973,25 +976,9 @@ int arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags,
 			     struct bpf_tramp_links *tlinks, void *func_addr)
 {
 	struct bpf_tramp_image im;
-	void *image;
 	int ret;
 
-	/*
-	 * Allocate a temporary buffer for __arch_prepare_bpf_trampoline().
-	 * This will NOT cause fragmentation in direct map, as we do not
-	 * call set_memory_*() on this buffer.
-	 *
-	 * We cannot use kvmalloc here, because we need image to be in
-	 * module memory range.
-	 */
-	image = bpf_jit_alloc_exec(PAGE_SIZE);
-	if (!image)
-		return -ENOMEM;
-
-	ret = __arch_prepare_bpf_trampoline(&im, image, image + PAGE_SIZE, image,
-					    m, flags, tlinks, func_addr);
-	bpf_jit_free_exec(image);
-
+	ret = __arch_prepare_bpf_trampoline(&im, NULL, NULL, NULL, m, flags, tlinks, func_addr);
 	return ret;
 }
 

arch/powerpc/net/bpf_jit_comp32.c

@@ -313,7 +313,6 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
 		u64 func_addr;
 		u32 true_cond;
 		u32 tmp_idx;
-		int j;
 
 		if (i && (BPF_CLASS(code) == BPF_ALU64 || BPF_CLASS(code) == BPF_ALU) &&
 		    (BPF_CLASS(prevcode) == BPF_ALU64 || BPF_CLASS(prevcode) == BPF_ALU) &&
@@ -1099,13 +1098,8 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
 		 * 16 byte instruction that uses two 'struct bpf_insn'
 		 */
 		case BPF_LD | BPF_IMM | BPF_DW: /* dst = (u64) imm */
-			tmp_idx = ctx->idx;
 			PPC_LI32(dst_reg_h, (u32)insn[i + 1].imm);
 			PPC_LI32(dst_reg, (u32)insn[i].imm);
-			/* padding to allow full 4 instructions for later patching */
-			if (!image)
-				for (j = ctx->idx - tmp_idx; j < 4; j++)
-					EMIT(PPC_RAW_NOP());
 			/* Adjust for two bpf instructions */
 			addrs[++i] = ctx->idx * 4;
 			break;

arch/powerpc/net/bpf_jit_comp64.c

@@ -227,7 +227,14 @@ int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *
 #ifdef CONFIG_PPC_KERNEL_PCREL
 	reladdr = func_addr - local_paca->kernelbase;
 
-	if (reladdr < (long)SZ_8G && reladdr >= -(long)SZ_8G) {
+	/*
+	 * If fimage is NULL (the initial pass to find image size),
+	 * account for the maximum no. of instructions possible.
+	 */
+	if (!fimage) {
+		ctx->idx += 7;
+		return 0;
+	} else if (reladdr < (long)SZ_8G && reladdr >= -(long)SZ_8G) {
 		EMIT(PPC_RAW_LD(_R12, _R13, offsetof(struct paca_struct, kernelbase)));
 		/* Align for subsequent prefix instruction */
 		if (!IS_ALIGNED((unsigned long)fimage + CTX_NIA(ctx), 8))
@@ -412,7 +419,6 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
 		u64 imm64;
 		u32 true_cond;
 		u32 tmp_idx;
-		int j;
 
 		/*
 		 * addrs[] maps a BPF bytecode address into a real offset from
@@ -1046,12 +1052,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
 		case BPF_LD | BPF_IMM | BPF_DW: /* dst = (u64) imm */
 			imm64 = ((u64)(u32) insn[i].imm) |
 				    (((u64)(u32) insn[i+1].imm) << 32);
-			tmp_idx = ctx->idx;
 			PPC_LI64(dst_reg, imm64);
-			/* padding to allow full 5 instructions for later patching */
-			if (!image)
-				for (j = ctx->idx - tmp_idx; j < 5; j++)
-					EMIT(PPC_RAW_NOP());
 			/* Adjust for two bpf instructions */
 			addrs[++i] = ctx->idx * 4;
 			break;