riscv: Avoid unaligned access when relocating modules

With the C-extension regular 32bit instructions are not
necessarily aligned on 4-byte boundaries. RISC-V instructions
are in fact an ordered list of 16bit little-endian
"parcels", so access the instruction as such.

This should also make the code work in case someone builds
a big-endian RISC-V machine.
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20231101-module_relocations-v9-1-8dfa3483c400@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/module.c

@@ -27,68 +27,90 @@ static bool riscv_insn_valid_32bit_offset(ptrdiff_t val)
 #endif
 }
 
-static int apply_r_riscv_32_rela(struct module *me, u32 *location, Elf_Addr v)
+static int riscv_insn_rmw(void *location, u32 keep, u32 set)
+{
+	u16 *parcel = location;
+	u32 insn = (u32)le16_to_cpu(parcel[0]) | (u32)le16_to_cpu(parcel[1]) << 16;
+
+	insn &= keep;
+	insn |= set;
+
+	parcel[0] = cpu_to_le16(insn);
+	parcel[1] = cpu_to_le16(insn >> 16);
+	return 0;
+}
+
+static int riscv_insn_rvc_rmw(void *location, u16 keep, u16 set)
+{
+	u16 *parcel = location;
+	u16 insn = le16_to_cpu(*parcel);
+
+	insn &= keep;
+	insn |= set;
+
+	*parcel = cpu_to_le16(insn);
+	return 0;
+}
+
+static int apply_r_riscv_32_rela(struct module *me, void *location, Elf_Addr v)
 {
 	if (v != (u32)v) {
 		pr_err("%s: value %016llx out of range for 32-bit field\n",
 		       me->name, (long long)v);
 		return -EINVAL;
 	}
-	*location = v;
+	*(u32 *)location = v;
 	return 0;
 }
 
-static int apply_r_riscv_64_rela(struct module *me, u32 *location, Elf_Addr v)
+static int apply_r_riscv_64_rela(struct module *me, void *location, Elf_Addr v)
 {
 	*(u64 *)location = v;
 	return 0;
 }
 
-static int apply_r_riscv_branch_rela(struct module *me, u32 *location,
+static int apply_r_riscv_branch_rela(struct module *me, void *location,
 				     Elf_Addr v)
 {
-	ptrdiff_t offset = (void *)v - (void *)location;
+	ptrdiff_t offset = (void *)v - location;
 	u32 imm12 = (offset & 0x1000) << (31 - 12);
 	u32 imm11 = (offset & 0x800) >> (11 - 7);
 	u32 imm10_5 = (offset & 0x7e0) << (30 - 10);
 	u32 imm4_1 = (offset & 0x1e) << (11 - 4);
 
-	*location = (*location & 0x1fff07f) | imm12 | imm11 | imm10_5 | imm4_1;
-	return 0;
+	return riscv_insn_rmw(location, 0x1fff07f, imm12 | imm11 | imm10_5 | imm4_1);
 }
 
-static int apply_r_riscv_jal_rela(struct module *me, u32 *location,
+static int apply_r_riscv_jal_rela(struct module *me, void *location,
 				  Elf_Addr v)
 {
-	ptrdiff_t offset = (void *)v - (void *)location;
+	ptrdiff_t offset = (void *)v - location;
 	u32 imm20 = (offset & 0x100000) << (31 - 20);
 	u32 imm19_12 = (offset & 0xff000);
 	u32 imm11 = (offset & 0x800) << (20 - 11);
 	u32 imm10_1 = (offset & 0x7fe) << (30 - 10);
 
-	*location = (*location & 0xfff) | imm20 | imm19_12 | imm11 | imm10_1;
-	return 0;
+	return riscv_insn_rmw(location, 0xfff, imm20 | imm19_12 | imm11 | imm10_1);
 }
 
-static int apply_r_riscv_rvc_branch_rela(struct module *me, u32 *location,
+static int apply_r_riscv_rvc_branch_rela(struct module *me, void *location,
 					 Elf_Addr v)
 {
-	ptrdiff_t offset = (void *)v - (void *)location;
+	ptrdiff_t offset = (void *)v - location;
 	u16 imm8 = (offset & 0x100) << (12 - 8);
 	u16 imm7_6 = (offset & 0xc0) >> (6 - 5);
 	u16 imm5 = (offset & 0x20) >> (5 - 2);
 	u16 imm4_3 = (offset & 0x18) << (12 - 5);
 	u16 imm2_1 = (offset & 0x6) << (12 - 10);
 
-	*(u16 *)location = (*(u16 *)location & 0xe383) |
-		    imm8 | imm7_6 | imm5 | imm4_3 | imm2_1;
-	return 0;
+	return riscv_insn_rvc_rmw(location, 0xe383,
+			imm8 | imm7_6 | imm5 | imm4_3 | imm2_1);
 }
 
-static int apply_r_riscv_rvc_jump_rela(struct module *me, u32 *location,
+static int apply_r_riscv_rvc_jump_rela(struct module *me, void *location,
 				       Elf_Addr v)
 {
-	ptrdiff_t offset = (void *)v - (void *)location;
+	ptrdiff_t offset = (void *)v - location;
 	u16 imm11 = (offset & 0x800) << (12 - 11);
 	u16 imm10 = (offset & 0x400) >> (10 - 8);
 	u16 imm9_8 = (offset & 0x300) << (12 - 11);
@@ -98,16 +120,14 @@ static int apply_r_riscv_rvc_jump_rela(struct module *me, u32 *location,
 	u16 imm4 = (offset & 0x10) << (12 - 5);
 	u16 imm3_1 = (offset & 0xe) << (12 - 10);
 
-	*(u16 *)location = (*(u16 *)location & 0xe003) |
-		    imm11 | imm10 | imm9_8 | imm7 | imm6 | imm5 | imm4 | imm3_1;
-	return 0;
+	return riscv_insn_rvc_rmw(location, 0xe003,
+			imm11 | imm10 | imm9_8 | imm7 | imm6 | imm5 | imm4 | imm3_1);
 }
 
-static int apply_r_riscv_pcrel_hi20_rela(struct module *me, u32 *location,
+static int apply_r_riscv_pcrel_hi20_rela(struct module *me, void *location,
 					 Elf_Addr v)
 {
-	ptrdiff_t offset = (void *)v - (void *)location;
-	s32 hi20;
+	ptrdiff_t offset = (void *)v - location;
 
 	if (!riscv_insn_valid_32bit_offset(offset)) {
 		pr_err(
@@ -116,23 +136,20 @@ static int apply_r_riscv_pcrel_hi20_rela(struct module *me, u32 *location,
 		return -EINVAL;
 	}
 
-	hi20 = (offset + 0x800) & 0xfffff000;
-	*location = (*location & 0xfff) | hi20;
-	return 0;
+	return riscv_insn_rmw(location, 0xfff, (offset + 0x800) & 0xfffff000);
 }
 
-static int apply_r_riscv_pcrel_lo12_i_rela(struct module *me, u32 *location,
+static int apply_r_riscv_pcrel_lo12_i_rela(struct module *me, void *location,
 					   Elf_Addr v)
 {
 	/*
 	 * v is the lo12 value to fill. It is calculated before calling this
 	 * handler.
 	 */
-	*location = (*location & 0xfffff) | ((v & 0xfff) << 20);
-	return 0;
+	return riscv_insn_rmw(location, 0xfffff, (v & 0xfff) << 20);
 }
 
-static int apply_r_riscv_pcrel_lo12_s_rela(struct module *me, u32 *location,
+static int apply_r_riscv_pcrel_lo12_s_rela(struct module *me, void *location,
 					   Elf_Addr v)
 {
 	/*
@@ -142,15 +159,12 @@ static int apply_r_riscv_pcrel_lo12_s_rela(struct module *me, u32 *location,
 	u32 imm11_5 = (v & 0xfe0) << (31 - 11);
 	u32 imm4_0 = (v & 0x1f) << (11 - 4);
 
-	*location = (*location & 0x1fff07f) | imm11_5 | imm4_0;
-	return 0;
+	return riscv_insn_rmw(location, 0x1fff07f, imm11_5 | imm4_0);
 }
 
-static int apply_r_riscv_hi20_rela(struct module *me, u32 *location,
+static int apply_r_riscv_hi20_rela(struct module *me, void *location,
 				   Elf_Addr v)
 {
-	s32 hi20;
-
 	if (IS_ENABLED(CONFIG_CMODEL_MEDLOW)) {
 		pr_err(
 		  "%s: target %016llx can not be addressed by the 32-bit offset from PC = %p\n",
@@ -158,22 +172,20 @@ static int apply_r_riscv_hi20_rela(struct module *me, u32 *location,
 		return -EINVAL;
 	}
 
-	hi20 = ((s32)v + 0x800) & 0xfffff000;
-	*location = (*location & 0xfff) | hi20;
-	return 0;
+	return riscv_insn_rmw(location, 0xfff, ((s32)v + 0x800) & 0xfffff000);
 }
 
-static int apply_r_riscv_lo12_i_rela(struct module *me, u32 *location,
+static int apply_r_riscv_lo12_i_rela(struct module *me, void *location,
 				     Elf_Addr v)
 {
 	/* Skip medlow checking because of filtering by HI20 already */
 	s32 hi20 = ((s32)v + 0x800) & 0xfffff000;
 	s32 lo12 = ((s32)v - hi20);
-	*location = (*location & 0xfffff) | ((lo12 & 0xfff) << 20);
-	return 0;
+
+	return riscv_insn_rmw(location, 0xfffff, (lo12 & 0xfff) << 20);
 }
 
-static int apply_r_riscv_lo12_s_rela(struct module *me, u32 *location,
+static int apply_r_riscv_lo12_s_rela(struct module *me, void *location,
 				     Elf_Addr v)
 {
 	/* Skip medlow checking because of filtering by HI20 already */
@@ -181,20 +193,18 @@ static int apply_r_riscv_lo12_s_rela(struct module *me, u32 *location,
 	s32 lo12 = ((s32)v - hi20);
 	u32 imm11_5 = (lo12 & 0xfe0) << (31 - 11);
 	u32 imm4_0 = (lo12 & 0x1f) << (11 - 4);
-	*location = (*location & 0x1fff07f) | imm11_5 | imm4_0;
-	return 0;
+
+	return riscv_insn_rmw(location, 0x1fff07f, imm11_5 | imm4_0);
 }
 
-static int apply_r_riscv_got_hi20_rela(struct module *me, u32 *location,
+static int apply_r_riscv_got_hi20_rela(struct module *me, void *location,
 				       Elf_Addr v)
 {
-	ptrdiff_t offset = (void *)v - (void *)location;
-	s32 hi20;
+	ptrdiff_t offset = (void *)v - location;
 
 	/* Always emit the got entry */
 	if (IS_ENABLED(CONFIG_MODULE_SECTIONS)) {
-		offset = module_emit_got_entry(me, v);
-		offset = (void *)offset - (void *)location;
+		offset = (void *)module_emit_got_entry(me, v) - location;
 	} else {
 		pr_err(
 		  "%s: can not generate the GOT entry for symbol = %016llx from PC = %p\n",
@@ -202,22 +212,19 @@ static int apply_r_riscv_got_hi20_rela(struct module *me, u32 *location,
 		return -EINVAL;
 	}
 
-	hi20 = (offset + 0x800) & 0xfffff000;
-	*location = (*location & 0xfff) | hi20;
-	return 0;
+	return riscv_insn_rmw(location, 0xfff, (offset + 0x800) & 0xfffff000);
 }
 
-static int apply_r_riscv_call_plt_rela(struct module *me, u32 *location,
+static int apply_r_riscv_call_plt_rela(struct module *me, void *location,
 				       Elf_Addr v)
 {
-	ptrdiff_t offset = (void *)v - (void *)location;
+	ptrdiff_t offset = (void *)v - location;
 	u32 hi20, lo12;
 
 	if (!riscv_insn_valid_32bit_offset(offset)) {
 		/* Only emit the plt entry if offset over 32-bit range */
 		if (IS_ENABLED(CONFIG_MODULE_SECTIONS)) {
-			offset = module_emit_plt_entry(me, v);
-			offset = (void *)offset - (void *)location;
+			offset = (void *)module_emit_plt_entry(me, v) - location;
 		} else {
 			pr_err(
 			  "%s: target %016llx can not be addressed by the 32-bit offset from PC = %p\n",
@@ -228,15 +235,14 @@ static int apply_r_riscv_call_plt_rela(struct module *me, u32 *location,
 
 	hi20 = (offset + 0x800) & 0xfffff000;
 	lo12 = (offset - hi20) & 0xfff;
-	*location = (*location & 0xfff) | hi20;
-	*(location + 1) = (*(location + 1) & 0xfffff) | (lo12 << 20);
-	return 0;
+	riscv_insn_rmw(location, 0xfff, hi20);
+	return riscv_insn_rmw(location + 4, 0xfffff, lo12 << 20);
 }
 
-static int apply_r_riscv_call_rela(struct module *me, u32 *location,
+static int apply_r_riscv_call_rela(struct module *me, void *location,
 				   Elf_Addr v)
 {
-	ptrdiff_t offset = (void *)v - (void *)location;
+	ptrdiff_t offset = (void *)v - location;
 	u32 hi20, lo12;
 
 	if (!riscv_insn_valid_32bit_offset(offset)) {
@@ -248,18 +254,17 @@ static int apply_r_riscv_call_rela(struct module *me, u32 *location,
 
 	hi20 = (offset + 0x800) & 0xfffff000;
 	lo12 = (offset - hi20) & 0xfff;
-	*location = (*location & 0xfff) | hi20;
-	*(location + 1) = (*(location + 1) & 0xfffff) | (lo12 << 20);
-	return 0;
+	riscv_insn_rmw(location, 0xfff, hi20);
+	return riscv_insn_rmw(location + 4, 0xfffff, lo12 << 20);
 }
 
-static int apply_r_riscv_relax_rela(struct module *me, u32 *location,
+static int apply_r_riscv_relax_rela(struct module *me, void *location,
 				    Elf_Addr v)
 {
 	return 0;
 }
 
-static int apply_r_riscv_align_rela(struct module *me, u32 *location,
+static int apply_r_riscv_align_rela(struct module *me, void *location,
 				    Elf_Addr v)
 {
 	pr_err(
@@ -268,49 +273,49 @@ static int apply_r_riscv_align_rela(struct module *me, u32 *location,
 	return -EINVAL;
 }
 
-static int apply_r_riscv_add16_rela(struct module *me, u32 *location,
+static int apply_r_riscv_add16_rela(struct module *me, void *location,
 				    Elf_Addr v)
 {
 	*(u16 *)location += (u16)v;
 	return 0;
 }
 
-static int apply_r_riscv_add32_rela(struct module *me, u32 *location,
+static int apply_r_riscv_add32_rela(struct module *me, void *location,
 				    Elf_Addr v)
 {
 	*(u32 *)location += (u32)v;
 	return 0;
 }
 
-static int apply_r_riscv_add64_rela(struct module *me, u32 *location,
+static int apply_r_riscv_add64_rela(struct module *me, void *location,
 				    Elf_Addr v)
 {
 	*(u64 *)location += (u64)v;
 	return 0;
 }
 
-static int apply_r_riscv_sub16_rela(struct module *me, u32 *location,
+static int apply_r_riscv_sub16_rela(struct module *me, void *location,
 				    Elf_Addr v)
 {
 	*(u16 *)location -= (u16)v;
 	return 0;
 }
 
-static int apply_r_riscv_sub32_rela(struct module *me, u32 *location,
+static int apply_r_riscv_sub32_rela(struct module *me, void *location,
 				    Elf_Addr v)
 {
 	*(u32 *)location -= (u32)v;
 	return 0;
 }
 
-static int apply_r_riscv_sub64_rela(struct module *me, u32 *location,
+static int apply_r_riscv_sub64_rela(struct module *me, void *location,
 				    Elf_Addr v)
 {
 	*(u64 *)location -= (u64)v;
 	return 0;
 }
 
-static int (*reloc_handlers_rela[]) (struct module *me, u32 *location,
+static int (*reloc_handlers_rela[]) (struct module *me, void *location,
 				Elf_Addr v) = {
 	[R_RISCV_32]			= apply_r_riscv_32_rela,
 	[R_RISCV_64]			= apply_r_riscv_64_rela,
@@ -342,9 +347,9 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
 		       struct module *me)
 {
 	Elf_Rela *rel = (void *) sechdrs[relsec].sh_addr;
-	int (*handler)(struct module *me, u32 *location, Elf_Addr v);
+	int (*handler)(struct module *me, void *location, Elf_Addr v);
 	Elf_Sym *sym;
-	u32 *location;
+	void *location;
 	unsigned int i, type;
 	Elf_Addr v;
 	int res;