[PATCH 00/14] Use const whether we point to literal strings (take 1)

Julien Grall posted 14 patches 1 week, 1 day ago
Test gitlab-ci failed
Patches applied successfully (tree, apply log)
git fetch https://gitlab.com/xen-project/patchew/xen tags/patchew/20210405155713.29754-1-julien@xen.org
tools/console/client/main.c         |  4 +-
tools/console/daemon/io.c           | 10 ++--
tools/debugger/kdd/kdd.c            | 10 ++--
tools/firmware/hvmloader/util.c     |  4 +-
tools/firmware/hvmloader/util.h     |  4 +-
tools/include/xenguest.h            | 10 ++--
tools/libs/guest/xg_dom_core.c      |  8 ++--
tools/libs/guest/xg_dom_elfloader.c |  4 +-
tools/libs/guest/xg_dom_hvmloader.c |  2 +-
tools/libs/guest/xg_dom_x86.c       |  9 ++--
tools/libs/guest/xg_private.h       |  2 +-
tools/libs/stat/xenstat_linux.c     |  4 +-
tools/libs/stat/xenstat_qmp.c       | 12 ++---
tools/misc/xen-detect.c             |  2 +-
tools/misc/xenhypfs.c               |  6 +--
tools/xenmon/xenbaked.c             |  2 +-
tools/xentop/xentop.c               | 12 ++---
tools/xentrace/xenalyze.c           | 71 +++++++++++++++--------------
tools/xentrace/xenctx.c             |  4 +-
tools/xl/xl.h                       |  8 ++--
tools/xl/xl_console.c               |  2 +-
tools/xl/xl_utils.c                 |  4 +-
tools/xl/xl_utils.h                 |  4 +-
xen/arch/x86/mm/shadow/multi.c      | 12 ++---
xen/common/rangeset.c               |  2 +-
xen/common/sched/private.h          |  4 +-
xen/drivers/char/console.c          |  4 +-
xen/include/xen/rangeset.h          |  2 +-
28 files changed, 113 insertions(+), 109 deletions(-)

[PATCH 00/14] Use const whether we point to literal strings (take 1)

Posted by Julien Grall 1 week, 1 day ago
From: Julien Grall <jgrall@amazon.com>

Hi all,

By default, both Clang and GCC will happily compile C code where
non-const char * point to literal strings. This means the following
code will be accepted:

    char *str = "test";

    str[0] = 'a';

Literal strings will reside in rodata, so they are not modifiable.
This will result to an permission fault at runtime if the permissions
are enforced in the page-tables (this is the case in Xen).

I am not aware of code trying to modify literal strings in Xen.
However, there is a frequent use of non-const char * to point to
literal strings. Given the size of the codebase, there is a risk
to involuntarily introduce code that will modify literal strings.

Therefore it would be better to enforce using const when pointing
to such strings. Both GCC and Clang provide an option to warn
for such case (see -Wwrite-strings) and therefore could be used
by Xen.

This series doesn't yet make use of -Wwrite-strings because
the tree is not fully converted. Instead, it contains some easy
and likely non-controversial use const in the code.

The major blockers to enable -Wwrite-strings are the following:
    - xen/common/efi: union string is used in both const and
    non-const situation. It doesn't feel right to specific one member
    const and the other non-const.
    - libxl: the major block is the flexarray framework as we would use
    it with string (now const char*). I thought it would be possible to
    make the interface const, but it looks like there are a couple of
    places where we need to modify the content (such as in
    libxl_json.c).

Ideally, I would like to have -Wwrite-strings unconditionally used
tree-wide. But, some of the area may required some heavy refactoring.

One solution would be to enable it tree-wide but turned it off at a
directroy/file level.

Any opinions?

Cheers,

Julien Grall (14):
  xen: Constify the second parameter of rangeset_new()
  xen/sched: Constify name and opt_name in struct scheduler
  xen/x86: shadow: The return type of sh_audit_flags() should be const
  xen/char: console: Use const whenever we point to literal strings
  tools/libs: guest: Use const whenever we point to literal strings
  tools/libs: stat: Use const whenever we point to literal strings
  tools/xl: Use const whenever we point to literal strings
  tools/firmware: hvmloader: Use const in __bug() and __assert_failed()
  tools/console: Use const whenever we point to literal strings
  tools/kdd: Use const whenever we point to literal strings
  tools/misc: Use const whenever we point to literal strings
  tools/top: The string parameter in set_prompt() and set_delay() should
    be const
  tools/xenmon: xenbaked: Mark const the field text in stat_map_t
  tools/xentrace: Use const whenever we point to literal strings

 tools/console/client/main.c         |  4 +-
 tools/console/daemon/io.c           | 10 ++--
 tools/debugger/kdd/kdd.c            | 10 ++--
 tools/firmware/hvmloader/util.c     |  4 +-
 tools/firmware/hvmloader/util.h     |  4 +-
 tools/include/xenguest.h            | 10 ++--
 tools/libs/guest/xg_dom_core.c      |  8 ++--
 tools/libs/guest/xg_dom_elfloader.c |  4 +-
 tools/libs/guest/xg_dom_hvmloader.c |  2 +-
 tools/libs/guest/xg_dom_x86.c       |  9 ++--
 tools/libs/guest/xg_private.h       |  2 +-
 tools/libs/stat/xenstat_linux.c     |  4 +-
 tools/libs/stat/xenstat_qmp.c       | 12 ++---
 tools/misc/xen-detect.c             |  2 +-
 tools/misc/xenhypfs.c               |  6 +--
 tools/xenmon/xenbaked.c             |  2 +-
 tools/xentop/xentop.c               | 12 ++---
 tools/xentrace/xenalyze.c           | 71 +++++++++++++++--------------
 tools/xentrace/xenctx.c             |  4 +-
 tools/xl/xl.h                       |  8 ++--
 tools/xl/xl_console.c               |  2 +-
 tools/xl/xl_utils.c                 |  4 +-
 tools/xl/xl_utils.h                 |  4 +-
 xen/arch/x86/mm/shadow/multi.c      | 12 ++---
 xen/common/rangeset.c               |  2 +-
 xen/common/sched/private.h          |  4 +-
 xen/drivers/char/console.c          |  4 +-
 xen/include/xen/rangeset.h          |  2 +-
 28 files changed, 113 insertions(+), 109 deletions(-)

-- 
2.17.1


Re: [PATCH 00/14] Use const whether we point to literal strings (take 1)

Posted by Julien Grall 1 week ago
Hi,

On 05/04/2021 16:56, Julien Grall wrote:
> Julien Grall (14):
>    xen: Constify the second parameter of rangeset_new()
>    xen/sched: Constify name and opt_name in struct scheduler
>    xen/x86: shadow: The return type of sh_audit_flags() should be const >    tools/firmware: hvmloader: Use const in __bug() and __assert_failed()
>    tools/kdd: Use const whenever we point to literal strings
>    tools/xentrace: Use const whenever we point to literal strings

I have merged the above patches. The rest still needs some reviews or 
respin (for patch #4).

Cheers,

-- 
Julien Grall

Re: [PATCH 00/14] Use const whether we point to literal strings (take 1)

Posted by Jan Beulich 1 week ago
On 05.04.2021 17:56, Julien Grall wrote:
> From: Julien Grall <jgrall@amazon.com>
> 
> Hi all,
> 
> By default, both Clang and GCC will happily compile C code where
> non-const char * point to literal strings. This means the following
> code will be accepted:
> 
>     char *str = "test";
> 
>     str[0] = 'a';
> 
> Literal strings will reside in rodata, so they are not modifiable.
> This will result to an permission fault at runtime if the permissions
> are enforced in the page-tables (this is the case in Xen).
> 
> I am not aware of code trying to modify literal strings in Xen.
> However, there is a frequent use of non-const char * to point to
> literal strings. Given the size of the codebase, there is a risk
> to involuntarily introduce code that will modify literal strings.
> 
> Therefore it would be better to enforce using const when pointing
> to such strings. Both GCC and Clang provide an option to warn
> for such case (see -Wwrite-strings) and therefore could be used
> by Xen.
> 
> This series doesn't yet make use of -Wwrite-strings because
> the tree is not fully converted. Instead, it contains some easy
> and likely non-controversial use const in the code.
> 
> The major blockers to enable -Wwrite-strings are the following:
>     - xen/common/efi: union string is used in both const and
>     non-const situation. It doesn't feel right to specific one member
>     const and the other non-const.

I'd be happy to see a suggestion of how to avoid this in a not overly
intrusive way.

>     - libxl: the major block is the flexarray framework as we would use
>     it with string (now const char*). I thought it would be possible to
>     make the interface const, but it looks like there are a couple of
>     places where we need to modify the content (such as in
>     libxl_json.c).
> 
> Ideally, I would like to have -Wwrite-strings unconditionally used
> tree-wide. But, some of the area may required some heavy refactoring.
> 
> One solution would be to enable it tree-wide but turned it off at a
> directroy/file level.

At least as a transient approach I think this would make sense. EFI in
particular has other reasons already to specify a custom option
(-fshort-wchar).

Jan