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Elf loader: give temporary write access to user .text memory

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When the .elf file is loaded from disk, the kernel must be given write
access to the allocated .text section in the task's address environment.

The access is removed after the elf is loaded and relocations are done.

NOTE:
The reason this works for the ARM implementation, is that the ARM MMU
can be configured to give write access for the privileged mode, but
revoke write access for the user mode.

Regardless, it would be smart to revoke write access even for the
kernel, when the kernel does not need it. This framework allows doing
that, if someone wishes to take up the task.
This commit is contained in:
Ville Juven
2022-03-29 12:15:30 +03:00
committed by Masayuki Ishikawa
parent 0ba891c1b0
commit 9af8b740e6
8 changed files with 337 additions and 5 deletions
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4
binfmt/libelf/libelf.h
View File

@@ -290,7 +290,7 @@ int elf_addrenv_alloc(FAR struct elf_loadinfo_s *loadinfo, size_t textsize,
****************************************************************************/
#ifdef CONFIG_ARCH_ADDRENV
# define elf_addrenv_select(l) up_addrenv_select(&(l)->addrenv, &(l)->oldenv)
int elf_addrenv_select(FAR struct elf_loadinfo_s *loadinfo);
#endif
/****************************************************************************
@@ -308,7 +308,7 @@ int elf_addrenv_alloc(FAR struct elf_loadinfo_s *loadinfo, size_t textsize,
****************************************************************************/
#ifdef CONFIG_ARCH_ADDRENV
# define elf_addrenv_restore(l) up_addrenv_restore(&(l)->oldenv)
int elf_addrenv_restore(FAR struct elf_loadinfo_s *loadinfo);
#endif
/****************************************************************************

86
binfmt/libelf/libelf_addrenv.c
View File

@@ -145,6 +145,92 @@ int elf_addrenv_alloc(FAR struct elf_loadinfo_s *loadinfo, size_t textsize,
#endif
}
/****************************************************************************
* Name: elf_addrenv_restore
*
* Description:
* Restore the address environment before elf_addrenv_select() was called..
*
* Input Parameters:
* loadinfo - Load state information
*
* Returned Value:
* Zero (OK) on success; a negated errno value on failure.
*
****************************************************************************/
#ifdef CONFIG_ARCH_ADDRENV
int elf_addrenv_select(FAR struct elf_loadinfo_s *loadinfo)
{
int ret;
/* Instantiate the new address environment */
ret = up_addrenv_select(&loadinfo->addrenv, &loadinfo->oldenv);
if (ret < 0)
{
berr("ERROR: up_addrenv_select failed: %d\n", ret);
return ret;
}
/* Allow write access to .text */
ret = up_addrenv_text_enable_write(&loadinfo->addrenv);
if (ret < 0)
{
berr("ERROR: up_addrenv_text_enable_write failed: %d\n", ret);
return ret;
}
return OK;
}
#endif
/****************************************************************************
* Name: elf_addrenv_free
*
* Description:
* Release the address environment previously created by
* elf_addrenv_alloc(). This function is called only under certain error
* conditions after the module has been loaded but not yet started.
* After the module has been started, the address environment will
* automatically be freed when the module exits.
*
* Input Parameters:
* loadinfo - Load state information
*
* Returned Value:
* None.
*
****************************************************************************/
#ifdef CONFIG_ARCH_ADDRENV
int elf_addrenv_restore(FAR struct elf_loadinfo_s *loadinfo)
{
int ret;
/* Remove write access to .text */
ret = up_addrenv_text_disable_write(&loadinfo->addrenv);
if (ret < 0)
{
berr("ERROR: up_addrenv_text_disable_write failed: %d\n", ret);
return ret;
}
/* Restore the old address environment */
ret = up_addrenv_restore(&loadinfo->oldenv);
if (ret < 0)
{
berr("ERROR: up_addrenv_restore failed: %d\n", ret);
return ret;
}
return OK;
}
#endif
/****************************************************************************
* Name: elf_addrenv_free
*