modpost: work around unaligned data access error

With the latest binutils, modpost fails with a bus error on some
architectures such as ARM and sparc64.

Since binutils commit 1f1b5e506bf0 ("bfd/ELF: restrict file alignment
for object files"), the byte offset to each section (sh_offset) in
relocatable ELF is no longer guaranteed to be aligned.

modpost parses MODULE_DEVICE_TABLE() data structures, which are usually
located in the .rodata section. If it is not properly aligned, unaligned
access errors may occur.

To address the issue, this commit imports the get_unaligned() helper
from include/linux/unaligned.h.

The get_unaligned_native() helper caters to the endianness in addition
to handling the unaligned access.

I slightly refactored do_pcmcia_entry() and do_input() to avoid writing
back to an unaligned address. (We would need the put_unaligned() helper
to do that.)

The addend_*_rel() functions need similar adjustments because the .text
sections are not aligned either.

It seems that the .symtab, .rel.* and .rela.* sections are still aligned.
Keep normal pointer access for these sections to avoid unnecessary
performance costs.

Reported-by: Paulo Pisati <paolo.pisati@canonical.com>
Reported-by: Matthias Klose <doko@debian.org>
Closes: https://sourceware.org/bugzilla/show_bug.cgi?id=32435
Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Closes: https://sourceware.org/bugzilla/show_bug.cgi?id=32493
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>

diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index 2c7b76d..19ec72a 100644 (file)
--- a/scripts/mod/file2alias.c
+++ b/scripts/mod/file2alias.c
@@ -132,7 +132,8 @@ struct devtable {
  * based at address m.
  */
 #define DEF_FIELD(m, devid, f) \
-       typeof(((struct devid *)0)->f) f = TO_NATIVE(*(typeof(f) *)((m) + OFF_##devid##_##f))
+       typeof(((struct devid *)0)->f) f = \
+               get_unaligned_native((typeof(f) *)((m) + OFF_##devid##_##f))
 
 /* Define a variable f that holds the address of field f of struct devid
  * based at address m.  Due to the way typeof works, for a field of type
@@ -600,7 +601,7 @@ static void do_pnp_card_entry(struct module *mod, void *symval)
 static void do_pcmcia_entry(struct module *mod, void *symval)
 {
        char alias[256] = {};
-       unsigned int i;
+
        DEF_FIELD(symval, pcmcia_device_id, match_flags);
        DEF_FIELD(symval, pcmcia_device_id, manf_id);
        DEF_FIELD(symval, pcmcia_device_id, card_id);
@@ -609,10 +610,6 @@ static void do_pcmcia_entry(struct module *mod, void *symval)
        DEF_FIELD(symval, pcmcia_device_id, device_no);
        DEF_FIELD_ADDR(symval, pcmcia_device_id, prod_id_hash);
 
-       for (i=0; i<4; i++) {
-               (*prod_id_hash)[i] = TO_NATIVE((*prod_id_hash)[i]);
-       }
-
        ADD(alias, "m", match_flags & PCMCIA_DEV_ID_MATCH_MANF_ID,
            manf_id);
        ADD(alias, "c", match_flags & PCMCIA_DEV_ID_MATCH_CARD_ID,
@@ -623,10 +620,14 @@ static void do_pcmcia_entry(struct module *mod, void *symval)
            function);
        ADD(alias, "pfn", match_flags & PCMCIA_DEV_ID_MATCH_DEVICE_NO,
            device_no);
-       ADD(alias, "pa", match_flags & PCMCIA_DEV_ID_MATCH_PROD_ID1, (*prod_id_hash)[0]);
-       ADD(alias, "pb", match_flags & PCMCIA_DEV_ID_MATCH_PROD_ID2, (*prod_id_hash)[1]);
-       ADD(alias, "pc", match_flags & PCMCIA_DEV_ID_MATCH_PROD_ID3, (*prod_id_hash)[2]);
-       ADD(alias, "pd", match_flags & PCMCIA_DEV_ID_MATCH_PROD_ID4, (*prod_id_hash)[3]);
+       ADD(alias, "pa", match_flags & PCMCIA_DEV_ID_MATCH_PROD_ID1,
+           get_unaligned_native(*prod_id_hash + 0));
+       ADD(alias, "pb", match_flags & PCMCIA_DEV_ID_MATCH_PROD_ID2,
+           get_unaligned_native(*prod_id_hash + 1));
+       ADD(alias, "pc", match_flags & PCMCIA_DEV_ID_MATCH_PROD_ID3,
+           get_unaligned_native(*prod_id_hash + 2));
+       ADD(alias, "pd", match_flags & PCMCIA_DEV_ID_MATCH_PROD_ID4,
+           get_unaligned_native(*prod_id_hash + 3));
 
        module_alias_printf(mod, true, "pcmcia:%s", alias);
 }
@@ -654,10 +655,9 @@ static void do_input(char *alias,
 {
        unsigned int i;
 
-       for (i = min / BITS_PER_LONG; i < max / BITS_PER_LONG + 1; i++)
-               arr[i] = TO_NATIVE(arr[i]);
        for (i = min; i <= max; i++)
-               if (arr[i / BITS_PER_LONG] & (1ULL << (i%BITS_PER_LONG)))
+               if (get_unaligned_native(arr + i / BITS_PER_LONG) &
+                   (1ULL << (i % BITS_PER_LONG)))
                        sprintf(alias + strlen(alias), "%X,*", i);
 }
 

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 94ee492..7ea59dc 100644 (file)
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1138,9 +1138,9 @@ static Elf_Addr addend_386_rel(uint32_t *location, unsigned int r_type)
 {
        switch (r_type) {
        case R_386_32:
-               return TO_NATIVE(*location);
+               return get_unaligned_native(location);
        case R_386_PC32:
-               return TO_NATIVE(*location) + 4;
+               return get_unaligned_native(location) + 4;
        }
 
        return (Elf_Addr)(-1);
@@ -1161,24 +1161,24 @@ static Elf_Addr addend_arm_rel(void *loc, Elf_Sym *sym, unsigned int r_type)
        switch (r_type) {
        case R_ARM_ABS32:
        case R_ARM_REL32:
-               inst = TO_NATIVE(*(uint32_t *)loc);
+               inst = get_unaligned_native((uint32_t *)loc);
                return inst + sym->st_value;
        case R_ARM_MOVW_ABS_NC:
        case R_ARM_MOVT_ABS:
-               inst = TO_NATIVE(*(uint32_t *)loc);
+               inst = get_unaligned_native((uint32_t *)loc);
                offset = sign_extend32(((inst & 0xf0000) >> 4) | (inst & 0xfff),
                                       15);
                return offset + sym->st_value;
        case R_ARM_PC24:
        case R_ARM_CALL:
        case R_ARM_JUMP24:
-               inst = TO_NATIVE(*(uint32_t *)loc);
+               inst = get_unaligned_native((uint32_t *)loc);
                offset = sign_extend32((inst & 0x00ffffff) << 2, 25);
                return offset + sym->st_value + 8;
        case R_ARM_THM_MOVW_ABS_NC:
        case R_ARM_THM_MOVT_ABS:
-               upper = TO_NATIVE(*(uint16_t *)loc);
-               lower = TO_NATIVE(*((uint16_t *)loc + 1));
+               upper = get_unaligned_native((uint16_t *)loc);
+               lower = get_unaligned_native((uint16_t *)loc + 1);
                offset = sign_extend32(((upper & 0x000f) << 12) |
                                       ((upper & 0x0400) << 1) |
                                       ((lower & 0x7000) >> 4) |
@@ -1195,8 +1195,8 @@ static Elf_Addr addend_arm_rel(void *loc, Elf_Sym *sym, unsigned int r_type)
                 * imm11 = lower[10:0]
                 * imm32 = SignExtend(S:J2:J1:imm6:imm11:'0')
                 */
-               upper = TO_NATIVE(*(uint16_t *)loc);
-               lower = TO_NATIVE(*((uint16_t *)loc + 1));
+               upper = get_unaligned_native((uint16_t *)loc);
+               lower = get_unaligned_native((uint16_t *)loc + 1);
 
                sign = (upper >> 10) & 1;
                j1 = (lower >> 13) & 1;
@@ -1219,8 +1219,8 @@ static Elf_Addr addend_arm_rel(void *loc, Elf_Sym *sym, unsigned int r_type)
                 * I2    = NOT(J2 XOR S)
                 * imm32 = SignExtend(S:I1:I2:imm10:imm11:'0')
                 */
-               upper = TO_NATIVE(*(uint16_t *)loc);
-               lower = TO_NATIVE(*((uint16_t *)loc + 1));
+               upper = get_unaligned_native((uint16_t *)loc);
+               lower = get_unaligned_native((uint16_t *)loc + 1);
 
                sign = (upper >> 10) & 1;
                j1 = (lower >> 13) & 1;
@@ -1241,7 +1241,7 @@ static Elf_Addr addend_mips_rel(uint32_t *location, unsigned int r_type)
 {
        uint32_t inst;
 
-       inst = TO_NATIVE(*location);
+       inst = get_unaligned_native(location);
        switch (r_type) {
        case R_MIPS_LO16:
                return inst & 0xffff;

diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 8b72c22..ffd0a52 100644 (file)
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -65,6 +65,20 @@
 #define TO_NATIVE(x)   \
        (target_is_big_endian == host_is_big_endian ? x : bswap(x))
 
+#define __get_unaligned_t(type, ptr) ({                                        \
+       const struct { type x; } __attribute__((__packed__)) *__pptr =  \
+                                               (typeof(__pptr))(ptr);  \
+       __pptr->x;                                                      \
+})
+
+#define get_unaligned(ptr)     __get_unaligned_t(typeof(*(ptr)), (ptr))
+
+#define get_unaligned_native(ptr) \
+({ \
+       typeof(*(ptr)) _val = get_unaligned(ptr); \
+       TO_NATIVE(_val); \
+})
+
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
 
 #define strstarts(str, prefix) (strncmp(str, prefix, strlen(prefix)) == 0)