Re: [PATCH][next] nvmem: core: Fix unintentional sign extension issue
On 11/03/2021 09:53, Colin King wrote:
From: Colin Ian King
The shifting of the u8 integer buf[3] by 24 bits to the left will
be promoted to a 32 bit signed int and then sign-extended to a
u64. In the event that the top bit of buf[3] is set then all
then all the upper 32 bits of the u64 end up as also being set
because of the sign-extension. Fix this by casting buf[i] to
a u64 before the shift.
Addresses-Coverity: ("Unintended sign extension")
Fixes: 097eb1136ebb ("nvmem: core: Add functions to make number reading easy")
Signed-off-by: Colin Ian King
---
Applied thanks,
--srini
drivers/nvmem/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 635e3131eb5f..bca671ff4e54 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1693,7 +1693,7 @@ int nvmem_cell_read_variable_le_u64(struct device *dev,
const char *cell_id,
/* Copy w/ implicit endian conversion */
*val = 0;
for (i = 0; i < len; i++)
- *val |= buf[i] << (8 * i);
+ *val |= (uint64_t)buf[i] << (8 * i);
kfree(buf);
Re: [PATCH][next] nvmem: core: Fix unintentional sign extension issue
On 11/03/2021 17:12, Doug Anderson wrote:
> Hi,
>
> On Thu, Mar 11, 2021 at 1:53 AM Colin King wrote:
>>
>> From: Colin Ian King
>>
>> The shifting of the u8 integer buf[3] by 24 bits to the left will
>> be promoted to a 32 bit signed int and then sign-extended to a
>> u64. In the event that the top bit of buf[3] is set then all
>> then all the upper 32 bits of the u64 end up as also being set
>> because of the sign-extension. Fix this by casting buf[i] to
>> a u64 before the shift.
>>
>> Addresses-Coverity: ("Unintended sign extension")
>> Fixes: 097eb1136ebb ("nvmem: core: Add functions to make number reading
>> easy")
>> Signed-off-by: Colin Ian King
>> ---
>> drivers/nvmem/core.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Thanks! I had only tested the "u64" version to read smaller data and
> store it in a u64. From my understanding of C rules, without your
> patch it would have been even worse than just a sign extension though,
> right? Shifting "buf[i]" by more than 32 bits would just not have
> worked right.
yep, that's correct, I forgot to mention that issue too :-/
>
> In any case:
>
> Reviewed-by: Douglas Anderson
>
Re: [PATCH][next] nvmem: core: Fix unintentional sign extension issue
Hi,
On Thu, Mar 11, 2021 at 1:53 AM Colin King wrote:
>
> From: Colin Ian King
>
> The shifting of the u8 integer buf[3] by 24 bits to the left will
> be promoted to a 32 bit signed int and then sign-extended to a
> u64. In the event that the top bit of buf[3] is set then all
> then all the upper 32 bits of the u64 end up as also being set
> because of the sign-extension. Fix this by casting buf[i] to
> a u64 before the shift.
>
> Addresses-Coverity: ("Unintended sign extension")
> Fixes: 097eb1136ebb ("nvmem: core: Add functions to make number reading easy")
> Signed-off-by: Colin Ian King
> ---
> drivers/nvmem/core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Thanks! I had only tested the "u64" version to read smaller data and
store it in a u64. From my understanding of C rules, without your
patch it would have been even worse than just a sign extension though,
right? Shifting "buf[i]" by more than 32 bits would just not have
worked right.
In any case:
Reviewed-by: Douglas Anderson
[PATCH][next] nvmem: core: Fix unintentional sign extension issue
From: Colin Ian King
The shifting of the u8 integer buf[3] by 24 bits to the left will
be promoted to a 32 bit signed int and then sign-extended to a
u64. In the event that the top bit of buf[3] is set then all
then all the upper 32 bits of the u64 end up as also being set
because of the sign-extension. Fix this by casting buf[i] to
a u64 before the shift.
Addresses-Coverity: ("Unintended sign extension")
Fixes: 097eb1136ebb ("nvmem: core: Add functions to make number reading easy")
Signed-off-by: Colin Ian King
---
drivers/nvmem/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 635e3131eb5f..bca671ff4e54 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1693,7 +1693,7 @@ int nvmem_cell_read_variable_le_u64(struct device *dev,
const char *cell_id,
/* Copy w/ implicit endian conversion */
*val = 0;
for (i = 0; i < len; i++)
- *val |= buf[i] << (8 * i);
+ *val |= (uint64_t)buf[i] << (8 * i);
kfree(buf);
--
2.30.2
