[05/10] ide: Remove uninitialized_var() usage
diff mbox series

Message ID 20200603233203.1695403-6-keescook@chromium.org
State New
Headers show
Series
  • Remove uninitialized_var() macro
Related show

Commit Message

Kees Cook June 3, 2020, 11:31 p.m. UTC
Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings (e.g.
"unused variable"). If the compiler thinks it is uninitialized, either
simply initialize the variable or make compiler changes. As a precursor
to removing[2] this[3] macro[4], just remove this variable since it was
actually unused:

drivers/ide/ide-taskfile.c:232:34: warning: unused variable 'flags' [-Wunused-variable]
        unsigned long uninitialized_var(flags);
                                        ^

[1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
[2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
[3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
[4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/ide/ide-taskfile.c | 1 -
 1 file changed, 1 deletion(-)

Comments

Nick Desaulniers June 4, 2020, 7:29 p.m. UTC | #1
On Wed, Jun 3, 2020 at 4:32 PM Kees Cook <keescook@chromium.org> wrote:
>
> Using uninitialized_var() is dangerous as it papers over real bugs[1]
> (or can in the future), and suppresses unrelated compiler warnings (e.g.
> "unused variable"). If the compiler thinks it is uninitialized, either
> simply initialize the variable or make compiler changes. As a precursor
> to removing[2] this[3] macro[4], just remove this variable since it was
> actually unused:
>
> drivers/ide/ide-taskfile.c:232:34: warning: unused variable 'flags' [-Wunused-variable]
>         unsigned long uninitialized_var(flags);
>                                         ^
>
> [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
> [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
> [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
> [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
>
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Fixes ce1e518190ea ("ide: don't disable interrupts during kmap_atomic()")

> ---
>  drivers/ide/ide-taskfile.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/drivers/ide/ide-taskfile.c b/drivers/ide/ide-taskfile.c
> index aab6a10435b6..a26f85ab58a9 100644
> --- a/drivers/ide/ide-taskfile.c
> +++ b/drivers/ide/ide-taskfile.c
> @@ -229,7 +229,6 @@ void ide_pio_bytes(ide_drive_t *drive, struct ide_cmd *cmd,
>         ide_hwif_t *hwif = drive->hwif;
>         struct scatterlist *sg = hwif->sg_table;
>         struct scatterlist *cursg = cmd->cursg;
> -       unsigned long uninitialized_var(flags);
>         struct page *page;
>         unsigned int offset;
>         u8 *buf;
> --
> 2.25.1
>
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Kees Cook June 4, 2020, 8:20 p.m. UTC | #2
On Thu, Jun 04, 2020 at 12:29:17PM -0700, Nick Desaulniers wrote:
> On Wed, Jun 3, 2020 at 4:32 PM Kees Cook <keescook@chromium.org> wrote:
> >
> > Using uninitialized_var() is dangerous as it papers over real bugs[1]
> > (or can in the future), and suppresses unrelated compiler warnings (e.g.
> > "unused variable"). If the compiler thinks it is uninitialized, either
> > simply initialize the variable or make compiler changes. As a precursor
> > to removing[2] this[3] macro[4], just remove this variable since it was
> > actually unused:
> >
> > drivers/ide/ide-taskfile.c:232:34: warning: unused variable 'flags' [-Wunused-variable]
> >         unsigned long uninitialized_var(flags);
> >                                         ^
> >
> > [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
> > [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
> > [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
> > [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> >
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> 
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

Thanks for the reviews!

> Fixes ce1e518190ea ("ide: don't disable interrupts during kmap_atomic()")

I originally avoided adding Fixes tags because I didn't want these
changes backported into a -stable without -Wmaybe-uninitialized
disabled, but in these cases (variable removal), that actually does make
sense. Thanks!

-Kees
Nick Desaulniers June 4, 2020, 8:29 p.m. UTC | #3
On Thu, Jun 4, 2020 at 1:20 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, Jun 04, 2020 at 12:29:17PM -0700, Nick Desaulniers wrote:
> > On Wed, Jun 3, 2020 at 4:32 PM Kees Cook <keescook@chromium.org> wrote:
> > >
> > > Using uninitialized_var() is dangerous as it papers over real bugs[1]
> > > (or can in the future), and suppresses unrelated compiler warnings (e.g.
> > > "unused variable"). If the compiler thinks it is uninitialized, either
> > > simply initialize the variable or make compiler changes. As a precursor
> > > to removing[2] this[3] macro[4], just remove this variable since it was
> > > actually unused:
> > >
> > > drivers/ide/ide-taskfile.c:232:34: warning: unused variable 'flags' [-Wunused-variable]
> > >         unsigned long uninitialized_var(flags);
> > >                                         ^
> > >
> > > [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
> > > [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
> > > [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
> > > [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> > >
> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> >
> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
> Thanks for the reviews!
>
> > Fixes ce1e518190ea ("ide: don't disable interrupts during kmap_atomic()")
>
> I originally avoided adding Fixes tags because I didn't want these
> changes backported into a -stable without -Wmaybe-uninitialized
> disabled, but in these cases (variable removal), that actually does make
> sense. Thanks!

Saravana showed me a cool trick for quickly finding commits that
removed a particular identifier that I find faster than `git blame` or
vim-fugitive for the purpose of Fixes tags:
$ git log -S <string> <file>
I've added it to our wiki:
https://github.com/ClangBuiltLinux/linux/wiki/Command-line-tips-and-tricks#for-finding-which-commit-may-have-removed-a-string-try.
I should update the first tip; what was your suggestion for
constraining the search to the current remote?
Sedat Dilek June 4, 2020, 8:58 p.m. UTC | #4
On Thu, Jun 4, 2020 at 10:20 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, Jun 04, 2020 at 12:29:17PM -0700, Nick Desaulniers wrote:
> > On Wed, Jun 3, 2020 at 4:32 PM Kees Cook <keescook@chromium.org> wrote:
> > >
> > > Using uninitialized_var() is dangerous as it papers over real bugs[1]
> > > (or can in the future), and suppresses unrelated compiler warnings (e.g.
> > > "unused variable"). If the compiler thinks it is uninitialized, either
> > > simply initialize the variable or make compiler changes. As a precursor
> > > to removing[2] this[3] macro[4], just remove this variable since it was
> > > actually unused:
> > >
> > > drivers/ide/ide-taskfile.c:232:34: warning: unused variable 'flags' [-Wunused-variable]
> > >         unsigned long uninitialized_var(flags);
> > >                                         ^
> > >
> > > [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
> > > [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
> > > [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
> > > [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> > >
> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> >
> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
> Thanks for the reviews!
>
> > Fixes ce1e518190ea ("ide: don't disable interrupts during kmap_atomic()")
>
> I originally avoided adding Fixes tags because I didn't want these
> changes backported into a -stable without -Wmaybe-uninitialized
> disabled, but in these cases (variable removal), that actually does make
> sense. Thanks!
>

Fixes tag does not automatically mean it is "for-stable".

[1] says:

> Patches that fix a severe bug in a released kernel should be directed
> toward the stable maintainers by putting a line like this::
>
>   Cc: stable@vger.kernel.org

- Sedat -

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst#n299
Kees Cook June 15, 2020, 7:32 p.m. UTC | #5
On Thu, Jun 04, 2020 at 01:29:44PM -0700, Nick Desaulniers wrote:
> On Thu, Jun 4, 2020 at 1:20 PM Kees Cook <keescook@chromium.org> wrote:
> >
> > On Thu, Jun 04, 2020 at 12:29:17PM -0700, Nick Desaulniers wrote:
> > > On Wed, Jun 3, 2020 at 4:32 PM Kees Cook <keescook@chromium.org> wrote:
> > > >
> > > > Using uninitialized_var() is dangerous as it papers over real bugs[1]
> > > > (or can in the future), and suppresses unrelated compiler warnings (e.g.
> > > > "unused variable"). If the compiler thinks it is uninitialized, either
> > > > simply initialize the variable or make compiler changes. As a precursor
> > > > to removing[2] this[3] macro[4], just remove this variable since it was
> > > > actually unused:
> > > >
> > > > drivers/ide/ide-taskfile.c:232:34: warning: unused variable 'flags' [-Wunused-variable]
> > > >         unsigned long uninitialized_var(flags);
> > > >                                         ^
> > > >
> > > > [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
> > > > [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
> > > > [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
> > > > [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> > > >
> > > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > >
> > > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> >
> > Thanks for the reviews!
> >
> > > Fixes ce1e518190ea ("ide: don't disable interrupts during kmap_atomic()")
> >
> > I originally avoided adding Fixes tags because I didn't want these
> > changes backported into a -stable without -Wmaybe-uninitialized
> > disabled, but in these cases (variable removal), that actually does make
> > sense. Thanks!
> 
> Saravana showed me a cool trick for quickly finding commits that
> removed a particular identifier that I find faster than `git blame` or
> vim-fugitive for the purpose of Fixes tags:
> $ git log -S <string> <file>

Ah yes, I always have to look up "-S". Good reminder!

> I've added it to our wiki:
> https://github.com/ClangBuiltLinux/linux/wiki/Command-line-tips-and-tricks#for-finding-which-commit-may-have-removed-a-string-try.
> I should update the first tip; what was your suggestion for
> constraining the search to the current remote?

Ah cool. I've updated it now. It was really to narrow to a "known set of
tags", and Linus's tree's tags always start with "v".

Patch
diff mbox series

diff --git a/drivers/ide/ide-taskfile.c b/drivers/ide/ide-taskfile.c
index aab6a10435b6..a26f85ab58a9 100644
--- a/drivers/ide/ide-taskfile.c
+++ b/drivers/ide/ide-taskfile.c
@@ -229,7 +229,6 @@  void ide_pio_bytes(ide_drive_t *drive, struct ide_cmd *cmd,
 	ide_hwif_t *hwif = drive->hwif;
 	struct scatterlist *sg = hwif->sg_table;
 	struct scatterlist *cursg = cmd->cursg;
-	unsigned long uninitialized_var(flags);
 	struct page *page;
 	unsigned int offset;
 	u8 *buf;