[v8,1/4] elf: Properly align all PT_LOAD segments [BZ #28676]
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Commit Message
Linker may set p_align of a PT_LOAD segment larger than p_align of the
first PT_LOAD segment to satisfy a section alignment:
Elf file type is DYN (Shared object file)
Entry point 0x0
There are 10 program headers, starting at offset 64
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000834 0x0000000000000834 R E 0x1000
LOAD 0x0000000000000e00 0x0000000000001e00 0x0000000000001e00
0x0000000000000230 0x0000000000000230 RW 0x1000
LOAD 0x0000000000400000 0x0000000000400000 0x0000000000400000
0x0000000000000004 0x0000000000000008 RW 0x400000
...
Section to Segment mapping:
Segment Sections...
00 .note.gnu.property .note.gnu.build-id .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt .init .plt .plt.got .text .fini .rodata .eh_frame_hdr .eh_frame
01 .init_array .fini_array .data.rel.ro .dynamic .got .got.plt
02 .data .bss
We should align the first PT_LOAD segment to the maximum p_align of all
PT_LOAD segments, similar to the kernel commit:
commit ce81bb256a224259ab686742a6284930cbe4f1fa
Author: Chris Kennelly <ckennelly@google.com>
Date: Thu Oct 15 20:12:32 2020 -0700
fs/binfmt_elf: use PT_LOAD p_align values for suitable start address
---
elf/dl-load.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
Comments
On 18/01/2022 18:57, H.J. Lu wrote:
> Linker may set p_align of a PT_LOAD segment larger than p_align of the
> first PT_LOAD segment to satisfy a section alignment:
>
> Elf file type is DYN (Shared object file)
> Entry point 0x0
> There are 10 program headers, starting at offset 64
>
> Program Headers:
> Type Offset VirtAddr PhysAddr
> FileSiz MemSiz Flags Align
> LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
> 0x0000000000000834 0x0000000000000834 R E 0x1000
> LOAD 0x0000000000000e00 0x0000000000001e00 0x0000000000001e00
> 0x0000000000000230 0x0000000000000230 RW 0x1000
> LOAD 0x0000000000400000 0x0000000000400000 0x0000000000400000
> 0x0000000000000004 0x0000000000000008 RW 0x400000
> ...
>
> Section to Segment mapping:
> Segment Sections...
> 00 .note.gnu.property .note.gnu.build-id .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt .init .plt .plt.got .text .fini .rodata .eh_frame_hdr .eh_frame
> 01 .init_array .fini_array .data.rel.ro .dynamic .got .got.plt
> 02 .data .bss
>
> We should align the first PT_LOAD segment to the maximum p_align of all
> PT_LOAD segments, similar to the kernel commit:
>
> commit ce81bb256a224259ab686742a6284930cbe4f1fa
> Author: Chris Kennelly <ckennelly@google.com>
> Date: Thu Oct 15 20:12:32 2020 -0700
>
> fs/binfmt_elf: use PT_LOAD p_align values for suitable start address
LGTM, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> elf/dl-load.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index 12744caf91..5b0ff41ee1 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -1101,6 +1101,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> size_t nloadcmds = 0;
> bool has_holes = false;
> bool empty_dynamic = false;
> + ElfW(Addr) p_align_max = 0;
>
> /* The struct is initialized to zero so this is not necessary:
> l->l_ld = 0;
> @@ -1146,7 +1147,9 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
> c->dataend = ph->p_vaddr + ph->p_filesz;
> c->allocend = ph->p_vaddr + ph->p_memsz;
> - c->mapalign = ph->p_align;
> + /* Remember the maximum p_align. */
> + if (powerof2 (ph->p_align) && ph->p_align > p_align_max)
> + p_align_max = ph->p_align;
> c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
>
> /* Determine whether there is a gap between the last segment
> @@ -1221,6 +1224,10 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> goto lose;
> }
>
> + /* Align all PT_LOAD segments to the maximum p_align. */
> + for (size_t i = 0; i < nloadcmds; i++)
> + loadcmds[i].mapalign = p_align_max;
> +
> /* dlopen of an executable is not valid because it is not possible
> to perform proper relocations, handle static TLS, or run the
> ELF constructors. For PIE, the check needs the dynamic
@@ -1101,6 +1101,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
size_t nloadcmds = 0;
bool has_holes = false;
bool empty_dynamic = false;
+ ElfW(Addr) p_align_max = 0;
/* The struct is initialized to zero so this is not necessary:
l->l_ld = 0;
@@ -1146,7 +1147,9 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
c->dataend = ph->p_vaddr + ph->p_filesz;
c->allocend = ph->p_vaddr + ph->p_memsz;
- c->mapalign = ph->p_align;
+ /* Remember the maximum p_align. */
+ if (powerof2 (ph->p_align) && ph->p_align > p_align_max)
+ p_align_max = ph->p_align;
c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
/* Determine whether there is a gap between the last segment
@@ -1221,6 +1224,10 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
goto lose;
}
+ /* Align all PT_LOAD segments to the maximum p_align. */
+ for (size_t i = 0; i < nloadcmds; i++)
+ loadcmds[i].mapalign = p_align_max;
+
/* dlopen of an executable is not valid because it is not possible
to perform proper relocations, handle static TLS, or run the
ELF constructors. For PIE, the check needs the dynamic