[PATCH] drm/komeda: Fix bit check to import to value of proper type
Carsten Haitzler
carsten.haitzler at foss.arm.com
Thu Jan 21 12:22:47 UTC 2021
On 1/20/21 3:44 PM, Steven Price wrote:
> On 18/01/2021 14:20, carsten.haitzler at foss.arm.com wrote:
>> From: Carsten Haitzler <carsten.haitzler at arm.com>
>>
>> Another issue found by KASAN. The bit finding is bueried inside the
>
> NIT: s/bueried/buried/
Yup. typo not spotted by me. Thanks. Also - i spotted an accidental
whitespace change along the way so can fix both in a new patch.
>> dp_for_each_set_bit() macro (that passes on to for_each_set_bit() that
>> calls the bit stuff. These bit functions want an unsigned long pointer
>> as input and just dumbly casting leads to out-of-bounds accesses.
>> This fixes that.
>
> This seems like an underlying bug/lack of clear documentation for the
> underlying find_*_bit() functions. dp_for_each_set_bit() tries to do the
> right thing:
Correct. This was a general problem I spotted - the bit funcs were
written to want a unsigned long but were being used on u32's by just
casting the ptr to the type and this did indeed have technical issues.
> #define dp_for_each_set_bit(bit, mask) \
> for_each_set_bit((bit), ((unsigned long *)&(mask)), sizeof(mask)
> * 8)
>
> i.e. passing the actual size of type. However because of the case to
> unsigned long (and subsequent accesses using that type) the compiler is
> free to make accesses beyond the size of the variable (and indeed this
> is completely broken on big-endian). The implementation actually
> requires that the bitmap is really an array of unsigned long - no other
> type will work.
Precisely. So a bit loose. The bit funcs are used widely enough, so just
fixing this code here to pass in the expected type is probably the least
disruptive fix.
> So I think the fix should also include fixing the dp_for_each_set_bit()
> macro - the cast is bogus as it stands.
Yup. Removing the cast does indeed find more badness that needs fixing.
I'll do an updated patch with this.
> Doing that I also get warnings on komeda_pipeline::avail_comps and
> komeda_pipeline::supported_inputs - although I note there are other
> bitmasks mentioned.
>
> The other option is to fix dp_for_each_set_bit() itself using a little
> hack:
>
> - for_each_set_bit((bit), ((unsigned long *)&(mask)), sizeof(mask)
> * 8)
> + for_each_set_bit((bit), (&((unsigned long){mask})), sizeof(mask)
> * 8)
>
> With that I don't think you need any other change as the mask is actually
> in a new unsigned long on the stack.
That would be wonderful if it worked :). Unfortunately your above
proposal leads to:
./drivers/gpu/drm/arm/display/komeda/../include/malidp_utils.h:17:27:
error: lvalue required as unary ‘&’ operand
17 | for_each_set_bit((bit), (&((unsigned long)(mask))),
sizeof(mask) * 8)
| ^
./include/linux/bitops.h:34:30: note: in definition of macro
‘for_each_set_bit’
34 | (bit) = find_next_bit((addr), (size), (bit) + 1))
| ^~~~
drivers/gpu/drm/arm/display/komeda/komeda_pipeline_state.c:1243:2: note:
in expansion of macro ‘dp_for_each_set_bit’
1243 | dp_for_each_set_bit(id, disabling_comps) {
| ^~~~~~~~~~~~~~~~~~~
Basically can't take address of an "unnamed local var". :| That is with:
#define dp_for_each_set_bit(bit, mask) \
for_each_set_bit((bit), (&((unsigned long)(mask))),
sizeof(mask) * 8)
I could try have the dp_for_each macro create new local vars on its own
a bit like:
#define dp_for_each_set_bit(bit, mask) \
unsigned long __local_mask = mask; \
for_each_set_bit((bit), (&__local_mask), sizeof(mask) * 8)
But we all know where this leads... (multiple bad places with adding
warnings and potential and pitfalls that then lead with ever more
invasive changes to address like if code in future might do if (x)
dp_for_each...). I'd prefer to be able to write code more loosely (pass
in any time and it just does the right thing), but trying to balance
this with least disruption and ugliness.
> Steve
>
>>
>> Signed-off-by: Carsten Haitzler <carsten.haitzler at arm.com>
>> ---
>> .../drm/arm/display/komeda/komeda_pipeline_state.c | 14 ++++++++------
>> 1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git
>> a/drivers/gpu/drm/arm/display/komeda/komeda_pipeline_state.c
>> b/drivers/gpu/drm/arm/display/komeda/komeda_pipeline_state.c
>> index e8b1e15312d8..f7dddb9f015d 100644
>> --- a/drivers/gpu/drm/arm/display/komeda/komeda_pipeline_state.c
>> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_pipeline_state.c
>> @@ -1232,7 +1232,8 @@ komeda_pipeline_unbound_components(struct
>> komeda_pipeline *pipe,
>> struct komeda_pipeline_state *old =
>> priv_to_pipe_st(pipe->obj.state);
>> struct komeda_component_state *c_st;
>> struct komeda_component *c;
>> - u32 disabling_comps, id;
>> + u32 id;
>> + unsigned long disabling_comps;
>> WARN_ON(!old);
>> @@ -1262,7 +1263,6 @@ int komeda_release_unclaimed_resources(struct
>> komeda_pipeline *pipe,
>> st = komeda_pipeline_get_new_state(pipe, drm_st);
>> else
>> st = komeda_pipeline_get_state_and_set_crtc(pipe, drm_st,
>> NULL);
>> -
>
> NIT: Random white space change
>
>> if (WARN_ON(IS_ERR_OR_NULL(st)))
>> return -EINVAL;
>> @@ -1287,7 +1287,8 @@ bool komeda_pipeline_disable(struct
>> komeda_pipeline *pipe,
>> struct komeda_pipeline_state *old;
>> struct komeda_component *c;
>> struct komeda_component_state *c_st;
>> - u32 id, disabling_comps = 0;
>> + u32 id;
>> + unsigned long disabling_comps;
>> old = komeda_pipeline_get_old_state(pipe, old_state);
>> @@ -1297,7 +1298,7 @@ bool komeda_pipeline_disable(struct
>> komeda_pipeline *pipe,
>> disabling_comps = old->active_comps &
>> pipe->standalone_disabled_comps;
>> - DRM_DEBUG_ATOMIC("PIPE%d: active_comps: 0x%x, disabling_comps:
>> 0x%x.\n",
>> + DRM_DEBUG_ATOMIC("PIPE%d: active_comps: 0x%x, disabling_comps:
>> 0x%lx.\n",
>> pipe->id, old->active_comps, disabling_comps);
>> dp_for_each_set_bit(id, disabling_comps) {
>> @@ -1331,13 +1332,14 @@ void komeda_pipeline_update(struct
>> komeda_pipeline *pipe,
>> struct komeda_pipeline_state *new =
>> priv_to_pipe_st(pipe->obj.state);
>> struct komeda_pipeline_state *old;
>> struct komeda_component *c;
>> - u32 id, changed_comps = 0;
>> + u32 id;
>> + unsigned long changed_comps;
>> old = komeda_pipeline_get_old_state(pipe, old_state);
>> changed_comps = new->active_comps | old->active_comps;
>> - DRM_DEBUG_ATOMIC("PIPE%d: active_comps: 0x%x, changed: 0x%x.\n",
>> + DRM_DEBUG_ATOMIC("PIPE%d: active_comps: 0x%x, changed: 0x%lx.\n",
>> pipe->id, new->active_comps, changed_comps);
>> dp_for_each_set_bit(id, changed_comps) {
>>
>
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