On Tue, 6 Aug 2024 21:49:27 +0000
jeffxu@xxxxxxxxxxxx wrote:
> From: Jeff Xu <jeffxu@xxxxxxxxxxxx>
>
> Some legacy SVr4 apps might depend on page on address zero
> to be readable, however I can't find a reason that the page
> ever becomes writeable, so seal it.
>
> If there is a compain, we can make this configurable.
>
> Signed-off-by: Jeff Xu <jeffxu@xxxxxxxxxxxx>
> ---
> fs/binfmt_elf.c | 5 +++++
> include/linux/mm.h | 10 ++++++++++
> mm/mseal.c | 2 +-
> 3 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 19fa49cd9907..f839fa228509 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -1314,6 +1314,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
> emulate the SVr4 behavior. Sigh. */
> error = vm_mmap(NULL, 0, PAGE_SIZE, PROT_READ | PROT_EXEC,
> MAP_FIXED | MAP_PRIVATE, 0);
> +
> + retval = do_mseal(0, PAGE_SIZE, 0);
> + if (retval)
> + pr_warn("pid=%d, couldn't seal address 0, ret=%d.\n",
> + task_pid_nr(current), retval);
> }
>
> regs = current_pt_regs();
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index c4b238a20b76..a178c15812eb 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4201,4 +4201,14 @@ void vma_pgtable_walk_end(struct vm_area_struct *vma);
>
> int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
>
> +#ifdef CONFIG_64BIT
Strictly speaking, this should be
#if defined(CONFIG_64BIT) && defined(CONFIG_MMU)
But since we do not support any 64-bit architecture without MMU, I'm
just making this marginal note, so it can be found in ML archives if
needed.
Petr T
