lkml.org 
[lkml]   [2021]   [Apr]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v4 1/2] binfmt_flat: allow not offsetting data start
From
Date

On 17/4/21 11:10 am, Damien Le Moal wrote:
> Commit 2217b9826246 ("binfmt_flat: revert "binfmt_flat: don't offset
> the data start"") restored offsetting the start of the data section by
> a number of words defined by MAX_SHARED_LIBS. As a result, since
> MAX_SHARED_LIBS is never 0, a gap between the text and data sections
> always exists. For architectures which cannot support a such gap
> between the text and data sections (e.g. riscv nommu), flat binary
> programs cannot be executed.
>
> To allow an architecture to request no data start offset to allow for
> contiguous text and data sections for binaries flagged with
> FLAT_FLAG_RAM, introduce the new config option
> CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET. Using this new option, the
> macro DATA_START_OFFSET_WORDS is conditionally defined in binfmt_flat.c
> to MAX_SHARED_LIBS for architectures tolerating or needing the data
> start offset (CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET disabled case)
> and to 0 when CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET is enabled.
> DATA_START_OFFSET_WORDS is used in load_flat_file() to calculate the
> data section length and start position.
>
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> ---
> fs/Kconfig.binfmt | 3 +++
> fs/binfmt_flat.c | 19 ++++++++++++++-----
> 2 files changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
> index c6f1c8c1934e..06fb7a93a1bd 100644
> --- a/fs/Kconfig.binfmt
> +++ b/fs/Kconfig.binfmt
> @@ -112,6 +112,9 @@ config BINFMT_FLAT_ARGVP_ENVP_ON_STACK
> config BINFMT_FLAT_OLD_ALWAYS_RAM
> bool
>
> +config BINFMT_FLAT_NO_DATA_START_OFFSET
> + bool
> +
> config BINFMT_FLAT_OLD
> bool "Enable support for very old legacy flat binaries"
> depends on BINFMT_FLAT
> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
> index b9c658e0548e..1dc68dfba3e0 100644
> --- a/fs/binfmt_flat.c
> +++ b/fs/binfmt_flat.c
> @@ -74,6 +74,12 @@
> #define MAX_SHARED_LIBS (1)
> #endif
>
> +#ifdef CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET
> +#define DATA_START_OFFSET_WORDS (0)
> +#else
> +#define DATA_START_OFFSET_WORDS (MAX_SHARED_LIBS)
> +#endif
> +
> struct lib_info {
> struct {
> unsigned long start_code; /* Start of text segment */
> @@ -560,6 +566,7 @@ static int load_flat_file(struct linux_binprm *bprm,
> * it all together.
> */
> if (!IS_ENABLED(CONFIG_MMU) && !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) {
> +

Random white space change...
Don't worry about re-spinning though, I will just edit this chunk out.


> /*
> * this should give us a ROM ptr, but if it doesn't we don't
> * really care
> @@ -576,7 +583,8 @@ static int load_flat_file(struct linux_binprm *bprm,
> goto err;
> }
>
> - len = data_len + extra + MAX_SHARED_LIBS * sizeof(unsigned long);
> + len = data_len + extra +
> + DATA_START_OFFSET_WORDS * sizeof(unsigned long);
> len = PAGE_ALIGN(len);
> realdatastart = vm_mmap(NULL, 0, len,
> PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, 0);
> @@ -591,7 +599,7 @@ static int load_flat_file(struct linux_binprm *bprm,
> goto err;
> }
> datapos = ALIGN(realdatastart +
> - MAX_SHARED_LIBS * sizeof(unsigned long),
> + DATA_START_OFFSET_WORDS * sizeof(unsigned long),
> FLAT_DATA_ALIGN);
>
> pr_debug("Allocated data+bss+stack (%u bytes): %lx\n",
> @@ -622,7 +630,8 @@ static int load_flat_file(struct linux_binprm *bprm,
> memp_size = len;
> } else {
>
> - len = text_len + data_len + extra + MAX_SHARED_LIBS * sizeof(u32);
> + len = text_len + data_len + extra +
> + DATA_START_OFFSET_WORDS * sizeof(u32);
> len = PAGE_ALIGN(len);
> textpos = vm_mmap(NULL, 0, len,
> PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE, 0);
> @@ -638,7 +647,7 @@ static int load_flat_file(struct linux_binprm *bprm,
>
> realdatastart = textpos + ntohl(hdr->data_start);
> datapos = ALIGN(realdatastart +
> - MAX_SHARED_LIBS * sizeof(u32),
> + DATA_START_OFFSET_WORDS * sizeof(u32),
> FLAT_DATA_ALIGN);
>
> reloc = (__be32 __user *)
> @@ -714,7 +723,7 @@ static int load_flat_file(struct linux_binprm *bprm,
> ret = result;
> pr_err("Unable to read code+data+bss, errno %d\n", ret);
> vm_munmap(textpos, text_len + data_len + extra +
> - MAX_SHARED_LIBS * sizeof(u32));
> + DATA_START_OFFSET_WORDS * sizeof(u32));
> goto err;
> }
> }
>

Thanks, otherwise looks good.

Acked-by: Greg Ungerer <gerg@linux-m68k.org>

I will push this into my m68knommu tree, for-next branch.
I just carry the flat format changes in that tree now to make my life easier.

Regards
Greg

\
 
 \ /
  Last update: 2021-04-17 06:53    [W:0.055 / U:0.204 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site