Re: [PATCH v4 1/2] binfmt_flat: allow not offsetting data start

[Damien Le Moal]

On 2021/04/17 13:52, Greg Ungerer wrote:
> 
> 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@xxxxxxx>
>> ---
>>   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.

Oops. Sorry about that. I should have better checked :)

> 
> 
>>   		/*
>>   		 * 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@xxxxxxxxxxxxxx>
> 
> 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.

Great. Thanks !
Are you taking both patches or should Plamer take the riscv Kconfig change
through his tree ?


> 
> Regards
> Greg
> 
> 


-- 
Damien Le Moal
Western Digital Research