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binfmt_flat: allow not offsetting data start

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Commit 2217b98262 ("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>
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>
This commit is contained in:
Damien Le Moal 2021-04-17 10:10:08 +09:00 committed by Greg Ungerer
parent bf05bf16c7
commit 04d82a6d08
2 changed files with 16 additions and 5 deletions
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3
fs/Kconfig.binfmt
View File

@ -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

18
fs/binfmt_flat.c
View File

@ -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 */
@ -576,7 +582,8 @@ 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 +598,7 @@ 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 +629,8 @@ 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 +646,7 @@ 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 +722,7 @@ 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;
}
}