arm: Avoid UB in elf_machine_rel()
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Build for i686
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Commit Message
This recently came up during a cleanup to remove misaligned accesses
from the RISC-V port.
Link: https://sourceware.org/pipermail/libc-alpha/2022-June/139961.html
Suggested-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
--
I haven't build this one, as I'm just doing it locally and don't have
everything setup here.
---
sysdeps/arm/dl-machine.h | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
Comments
On 2022-06-23, Palmer Dabbelt wrote:
>This recently came up during a cleanup to remove misaligned accesses
>from the RISC-V port.
>
>Link: https://sourceware.org/pipermail/libc-alpha/2022-June/139961.html
>Suggested-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
>Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
LGTM
Reviewed-by: Fangrui Song <maskray@google.com>
>--
>
>I haven't build this one, as I'm just doing it locally and don't have
>everything setup here.
>---
> sysdeps/arm/dl-machine.h | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
>diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h
>index 68dcb96d9d..6bb3917340 100644
>--- a/sysdeps/arm/dl-machine.h
>+++ b/sysdeps/arm/dl-machine.h
>@@ -402,10 +402,7 @@ elf_machine_rel (struct link_map *map, struct r_scope_elem *scope[],
> break;
> case R_ARM_ABS32:
> {
>- struct unaligned
>- {
>- Elf32_Addr x;
>- } __attribute__ ((packed, may_alias));
>+ ElfW(Addr) tmp;
> # ifndef RTLD_BOOTSTRAP
> /* This is defined in rtld.c, but nowhere in the static
> libc.a; make the reference weak so static programs can
>@@ -425,7 +422,9 @@ elf_machine_rel (struct link_map *map, struct r_scope_elem *scope[],
> value -= SYMBOL_ADDRESS (map, refsym, true);
> # endif
> /* Support relocations on mis-aligned offsets. */
>- ((struct unaligned *) reloc_addr)->x += value;
>+ memcpy(&tmp, reloc_addr, sizeof tmp);
>+ tmp += value;
>+ memcpy (reloc_addr, &tmp, sizeof tmp);
> break;
> }
> case R_ARM_TLS_DESC:
>--
>2.34.1
>
@@ -402,10 +402,7 @@ elf_machine_rel (struct link_map *map, struct r_scope_elem *scope[],
break;
case R_ARM_ABS32:
{
- struct unaligned
- {
- Elf32_Addr x;
- } __attribute__ ((packed, may_alias));
+ ElfW(Addr) tmp;
# ifndef RTLD_BOOTSTRAP
/* This is defined in rtld.c, but nowhere in the static
libc.a; make the reference weak so static programs can
@@ -425,7 +422,9 @@ elf_machine_rel (struct link_map *map, struct r_scope_elem *scope[],
value -= SYMBOL_ADDRESS (map, refsym, true);
# endif
/* Support relocations on mis-aligned offsets. */
- ((struct unaligned *) reloc_addr)->x += value;
+ memcpy(&tmp, reloc_addr, sizeof tmp);
+ tmp += value;
+ memcpy (reloc_addr, &tmp, sizeof tmp);
break;
}
case R_ARM_TLS_DESC: