| Message ID | 20200603233203.1695403-4-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
| Series | Remove uninitialized_var() macro | expand |
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 initialize this variable to NULL, > and make the (unreachable!) code do a conditional test. > > [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/net/wireless/broadcom/b43/phy_n.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c > index d3c001fa8eb4..88cdcea10d61 100644 > --- a/drivers/net/wireless/broadcom/b43/phy_n.c > +++ b/drivers/net/wireless/broadcom/b43/phy_n.c > @@ -4222,7 +4222,7 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) The TODOs and `#if 0` in this function are concerning. It looks like `rf_pwr_offset_table` is only used when `phy->rev` is >=7 && < 19. Further, the loop has a case for `phy->rev >= 19` but we would have returned earlier if that was the case. > u32 rfpwr_offset; > u8 pga_gain, pad_gain; > int i; > - const s16 *uninitialized_var(rf_pwr_offset_table); > + const s16 *rf_pwr_offset_table = NULL; > > table = b43_nphy_get_tx_gain_table(dev); > if (!table) > @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) > pga_gain = (table[i] >> 24) & 0xf; > pad_gain = (table[i] >> 19) & 0x1f; > if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ) > - rfpwr_offset = rf_pwr_offset_table[pad_gain]; > + rfpwr_offset = rf_pwr_offset_table > + ? rf_pwr_offset_table[pad_gain] > + : 0; > else > - rfpwr_offset = rf_pwr_offset_table[pga_gain]; > + rfpwr_offset = rf_pwr_offset_table > + ? rf_pwr_offset_table[pga_gain] > + : 0; The code is trying to check `phy->rev >= 7 && phy->rev < 19` once before the loop, then set `rf_pwr_offset_table`, so having another conditional on `rf_pwr_offset_table` in the loop is unnecessary. I'm ok with initializing it to `NULL`, but I'm not sure the conditional check is necessary. Do you get a compiler warning otherwise? > } else { > pga_gain = (table[i] >> 24) & 0xF; > if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ) > -- > 2.25.1 > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20200603233203.1695403-4-keescook%40chromium.org.
On Thu, Jun 04, 2020 at 01:08:44PM -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 initialize this variable to NULL, > > and make the (unreachable!) code do a conditional test. > > > > [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/net/wireless/broadcom/b43/phy_n.c | 10 +++++++--- > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c > > index d3c001fa8eb4..88cdcea10d61 100644 > > --- a/drivers/net/wireless/broadcom/b43/phy_n.c > > +++ b/drivers/net/wireless/broadcom/b43/phy_n.c > > @@ -4222,7 +4222,7 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) > > The TODOs and `#if 0` in this function are concerning. It looks like > `rf_pwr_offset_table` is only used when `phy->rev` is >=7 && < 19. > > Further, the loop has a case for `phy->rev >= 19` but we would have > returned earlier if that was the case. Yeah, that's why I put the "(unreachable!)" note in the commit log. ;) > > > u32 rfpwr_offset; > > u8 pga_gain, pad_gain; > > int i; > > - const s16 *uninitialized_var(rf_pwr_offset_table); > > + const s16 *rf_pwr_offset_table = NULL; > > > > table = b43_nphy_get_tx_gain_table(dev); > > if (!table) > > @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) > > pga_gain = (table[i] >> 24) & 0xf; > > pad_gain = (table[i] >> 19) & 0x1f; > > if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ) > > - rfpwr_offset = rf_pwr_offset_table[pad_gain]; > > + rfpwr_offset = rf_pwr_offset_table > > + ? rf_pwr_offset_table[pad_gain] > > + : 0; > > else > > - rfpwr_offset = rf_pwr_offset_table[pga_gain]; > > + rfpwr_offset = rf_pwr_offset_table > > + ? rf_pwr_offset_table[pga_gain] > > + : 0; > > > The code is trying to check `phy->rev >= 7 && phy->rev < 19` once > before the loop, then set `rf_pwr_offset_table`, so having another > conditional on `rf_pwr_offset_table` in the loop is unnecessary. I'm > ok with initializing it to `NULL`, but I'm not sure the conditional > check is necessary. Do you get a compiler warning otherwise? I mean, sort of the best thing to do is just remove nearly everything here since it's actually unreachable. But it is commented as "when supported ..." etc, so I figured I'd leave it. As part of that I didn't want to leave any chance of a NULL deref, so I added the explicit tests just for robustness. *shrug* -Kees
On Thu, Jun 4, 2020 at 1:18 PM Kees Cook <keescook@chromium.org> wrote: > > On Thu, Jun 04, 2020 at 01:08:44PM -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 initialize this variable to NULL, > > > and make the (unreachable!) code do a conditional test. > > > > > > [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/net/wireless/broadcom/b43/phy_n.c | 10 +++++++--- > > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > > > diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c > > > index d3c001fa8eb4..88cdcea10d61 100644 > > > --- a/drivers/net/wireless/broadcom/b43/phy_n.c > > > +++ b/drivers/net/wireless/broadcom/b43/phy_n.c > > > @@ -4222,7 +4222,7 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) > > > > The TODOs and `#if 0` in this function are concerning. It looks like > > `rf_pwr_offset_table` is only used when `phy->rev` is >=7 && < 19. > > > > Further, the loop has a case for `phy->rev >= 19` but we would have > > returned earlier if that was the case. oh, and there's an early return for `phy->rev < 3` I just noticed. > > Yeah, that's why I put the "(unreachable!)" note in the commit log. ;) I don't think that note is correct. > > > > > > u32 rfpwr_offset; > > > u8 pga_gain, pad_gain; > > > int i; > > > - const s16 *uninitialized_var(rf_pwr_offset_table); > > > + const s16 *rf_pwr_offset_table = NULL; > > > > > > table = b43_nphy_get_tx_gain_table(dev); > > > if (!table) > > > @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) > > > pga_gain = (table[i] >> 24) & 0xf; > > > pad_gain = (table[i] >> 19) & 0x1f; > > > if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ) > > > - rfpwr_offset = rf_pwr_offset_table[pad_gain]; > > > + rfpwr_offset = rf_pwr_offset_table > > > + ? rf_pwr_offset_table[pad_gain] > > > + : 0; > > > else > > > - rfpwr_offset = rf_pwr_offset_table[pga_gain]; > > > + rfpwr_offset = rf_pwr_offset_table > > > + ? rf_pwr_offset_table[pga_gain] > > > + : 0; > > > > > > The code is trying to check `phy->rev >= 7 && phy->rev < 19` once > > before the loop, then set `rf_pwr_offset_table`, so having another > > conditional on `rf_pwr_offset_table` in the loop is unnecessary. I'm > > ok with initializing it to `NULL`, but I'm not sure the conditional > > check is necessary. Do you get a compiler warning otherwise? > > I mean, sort of the best thing to do is just remove nearly everything > here since it's actually unreachable. But it is commented as "when This code is reachable. Consider `phy->rev >= 7 && phy->rev < 19`. If `rf_pwr_offset_table` was NULL, it would have returned early on L4246, so the checks added in this patch are unnecessary. Forgive me if there's some other control flow I'm not considering. > supported ..." etc, so I figured I'd leave it. As part of that I didn't > want to leave any chance of a NULL deref, so I added the explicit tests > just for robustness. > > *shrug*
Kees Cook <keescook@chromium.org> writes: > 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 initialize this variable to NULL, > and make the (unreachable!) code do a conditional test. > > [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> [...] > @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) > pga_gain = (table[i] >> 24) & 0xf; > pad_gain = (table[i] >> 19) & 0x1f; > if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ) > - rfpwr_offset = rf_pwr_offset_table[pad_gain]; > + rfpwr_offset = rf_pwr_offset_table > + ? rf_pwr_offset_table[pad_gain] > + : 0; > else > - rfpwr_offset = rf_pwr_offset_table[pga_gain]; > + rfpwr_offset = rf_pwr_offset_table > + ? rf_pwr_offset_table[pga_gain] > + : 0; To me this is ugly, isn't there a better way to fix this?
diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c index d3c001fa8eb4..88cdcea10d61 100644 --- a/drivers/net/wireless/broadcom/b43/phy_n.c +++ b/drivers/net/wireless/broadcom/b43/phy_n.c @@ -4222,7 +4222,7 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) u32 rfpwr_offset; u8 pga_gain, pad_gain; int i; - const s16 *uninitialized_var(rf_pwr_offset_table); + const s16 *rf_pwr_offset_table = NULL; table = b43_nphy_get_tx_gain_table(dev); if (!table) @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) pga_gain = (table[i] >> 24) & 0xf; pad_gain = (table[i] >> 19) & 0x1f; if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ) - rfpwr_offset = rf_pwr_offset_table[pad_gain]; + rfpwr_offset = rf_pwr_offset_table + ? rf_pwr_offset_table[pad_gain] + : 0; else - rfpwr_offset = rf_pwr_offset_table[pga_gain]; + rfpwr_offset = rf_pwr_offset_table + ? rf_pwr_offset_table[pga_gain] + : 0; } else { pga_gain = (table[i] >> 24) & 0xF; if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ)
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 initialize this variable to NULL, and make the (unreachable!) code do a conditional test. [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/net/wireless/broadcom/b43/phy_n.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)