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Subject[PATCH v1 1/2] riscv: Avoid unaligned access when relocating modules
Date
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 native-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.

Fix rcv -> rvc typo while we're at it.

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
---
arch/riscv/kernel/module.c | 155 +++++++++++++++++++------------------
1 file changed, 79 insertions(+), 76 deletions(-)

diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
index 104fba889cf7..05b2162d96be 100644
--- a/arch/riscv/kernel/module.c
+++ b/arch/riscv/kernel/module.c
@@ -13,68 +13,86 @@
#include <linux/pgtable.h>
#include <asm/sections.h>

-static int apply_r_riscv_32_rela(struct module *me, u32 *location, Elf_Addr v)
+static int riscv_insn_rmw(u8 *location, u32 keep, u32 set)
+{
+ u16 *parcel = (u16 *)location;
+ u32 insn = (u32)parcel[0] | (u32)parcel[1] << 16;
+
+ insn &= keep;
+ insn |= set;
+
+ parcel[0] = insn;
+ parcel[1] = insn >> 16;
+ return 0;
+}
+
+static int riscv_insn_rvc_rmw(u8 *location, u16 keep, u16 set)
+{
+ u16 *parcel = (u16 *)location;
+
+ *parcel = (*parcel & keep) | set;
+ return 0;
+}
+
+static int apply_r_riscv_32_rela(struct module *me, u8 *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, u8 *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, u8 *location,
Elf_Addr v)
{
- ptrdiff_t offset = (void *)v - (void *)location;
+ ptrdiff_t offset = (u8 *)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, u8 *location,
Elf_Addr v)
{
- ptrdiff_t offset = (void *)v - (void *)location;
+ ptrdiff_t offset = (u8 *)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_rcv_branch_rela(struct module *me, u32 *location,
+static int apply_r_riscv_rvc_branch_rela(struct module *me, u8 *location,
Elf_Addr v)
{
- ptrdiff_t offset = (void *)v - (void *)location;
+ ptrdiff_t offset = (u8 *)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, u8 *location,
Elf_Addr v)
{
- ptrdiff_t offset = (void *)v - (void *)location;
+ ptrdiff_t offset = (u8 *)v - location;
u16 imm11 = (offset & 0x800) << (12 - 11);
u16 imm10 = (offset & 0x400) >> (10 - 8);
u16 imm9_8 = (offset & 0x300) << (12 - 11);
@@ -84,16 +102,14 @@ 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, u8 *location,
Elf_Addr v)
{
- ptrdiff_t offset = (void *)v - (void *)location;
- s32 hi20;
+ ptrdiff_t offset = (u8 *)v - location;

if (offset != (s32)offset) {
pr_err(
@@ -102,23 +118,20 @@ 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, u8 *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, u8 *location,
Elf_Addr v)
{
/*
@@ -128,15 +141,12 @@ 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, u8 *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",
@@ -144,22 +154,20 @@ 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, u8 *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, u8 *location,
Elf_Addr v)
{
/* Skip medlow checking because of filtering by HI20 already */
@@ -167,20 +175,19 @@ 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, u8 *location,
Elf_Addr v)
{
- ptrdiff_t offset = (void *)v - (void *)location;
- s32 hi20;
+ ptrdiff_t offset = (u8 *)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;
+ unsigned long entry = module_emit_got_entry(me, v);
+ offset = (u8 *)entry - location;
} else {
pr_err(
"%s: can not generate the GOT entry for symbol = %016llx from PC = %p\n",
@@ -188,23 +195,21 @@ 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, u8 *location,
Elf_Addr v)
{
- ptrdiff_t offset = (void *)v - (void *)location;
+ ptrdiff_t offset = (u8 *)v - location;
s32 fill_v = offset;
u32 hi20, lo12;

if (offset != fill_v) {
/* 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;
+ unsigned long entry = module_emit_plt_entry(me, v);
+ offset = (u8 *)entry - location;
} else {
pr_err(
"%s: target %016llx can not be addressed by the 32-bit offset from PC = %p\n",
@@ -215,15 +220,14 @@ 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, u8 *location,
Elf_Addr v)
{
- ptrdiff_t offset = (void *)v - (void *)location;
+ ptrdiff_t offset = (u8 *)v - location;
s32 fill_v = offset;
u32 hi20, lo12;

@@ -236,18 +240,17 @@ 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, u8 *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, u8 *location,
Elf_Addr v)
{
pr_err(
@@ -256,41 +259,41 @@ static int apply_r_riscv_align_rela(struct module *me, u32 *location,
return -EINVAL;
}

-static int apply_r_riscv_add32_rela(struct module *me, u32 *location,
+static int apply_r_riscv_add32_rela(struct module *me, u8 *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, u8 *location,
Elf_Addr v)
{
*(u64 *)location += (u64)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, u8 *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, u8 *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, u8 *location,
Elf_Addr v) = {
[R_RISCV_32] = apply_r_riscv_32_rela,
[R_RISCV_64] = apply_r_riscv_64_rela,
[R_RISCV_BRANCH] = apply_r_riscv_branch_rela,
[R_RISCV_JAL] = apply_r_riscv_jal_rela,
- [R_RISCV_RVC_BRANCH] = apply_r_riscv_rcv_branch_rela,
+ [R_RISCV_RVC_BRANCH] = apply_r_riscv_rvc_branch_rela,
[R_RISCV_RVC_JUMP] = apply_r_riscv_rvc_jump_rela,
[R_RISCV_PCREL_HI20] = apply_r_riscv_pcrel_hi20_rela,
[R_RISCV_PCREL_LO12_I] = apply_r_riscv_pcrel_lo12_i_rela,
@@ -314,9 +317,9 @@ 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, u8 *location, Elf_Addr v);
Elf_Sym *sym;
- u32 *location;
+ u8 *location;
unsigned int i, type;
Elf_Addr v;
int res;
@@ -326,7 +329,7 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,

for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
/* This is where to make the change */
- location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+ location = (u8 *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+ rel[i].r_offset;
/* This is the symbol it is referring to */
sym = (Elf_Sym *)sechdrs[symindex].sh_addr
--
2.27.0
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