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

On Thu, 22 Apr 2021 22:38:36 PDT (-0700), [email protected] wrote:
>
>
> On 23/4/21 2:04 pm, Palmer Dabbelt wrote:
>> On Thu, 22 Apr 2021 05:00:32 PDT (-0700), Damien Le Moal wrote:
>>>> On 2021/04/18 11:38, Greg Ungerer wrote:
>>>>
>>>>
>>>> On 17/4/21 2:54 pm, Damien Le Moal wrote:
>>>>> 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 <[email protected]>
>>>>>>> ---
>>>>>>>    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 <[email protected]>
>>>>>>
>>>>>> 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 ?
>>>>
>>>> I am happy to take both.
>>>> Palmer?
>>>
>>> Palmer,
>>>
>>> Ping !
>>
>> I already Ack'd it, in the thread where we couldn't find the maintainer. Keeping these togther is fine with me, and it seems easiest.
>
> The 2/2 patch has been applied to the m68knommu git tree, for-next branch.

Thanks!