Re: [PATCH v3] RAS/AMD/ATL: Fix unintended sign extension issue from coverity

[Borislav Petkov]

On Wed, Dec 11, 2024 at 11:01:13AM -0500, Yazen Ghannam wrote:
> On Wed, Nov 27, 2024 at 06:23:48PM +0000, Karan Sanghavi wrote:
> > This error is reported by coverity scan stating as
> > 
> > CID 1593397: (#1 of 1): Unintended sign extension (SIGN_EXTENSION)
> > sign_extension: Suspicious implicit sign extension: pc
> > with type u16 (16 bits, unsigned) is promoted in
> > pc << bit_shifts.pc to type int (32 bits, signed),
> > then sign-extended to type unsigned long (64 bits, unsigned).
> > If pc << bit_shifts.pc is greater than 0x7FFFFFFF,
> > the upper bits of the result will all be 1.
> > 
> > Use u32 for bitwise operations to prevent unintentional
> > sign extension by assigning the u16 value to a u32
> > variable before performing the bitwise operation to
> > avoid unintended sign extension and maintain
> > consistency with the existing code style.
> > 
> > Reviewed-by: Yazen Ghannam <yazen.ghannam@xxxxxxx>
> > Signed-off-by: Karan Sanghavi <karansanghvi98@xxxxxxxxx>

> Boris, can you please take this patch if no objections?

Lemme see:

bit_shifts.pc     = 5 + FIELD_GET(ADDR_SEL_2_CHAN, temp);

#define ADDR_SEL_2_CHAN         GENMASK(15, 12)

that register field is 4 bits, so 0xf is the highest value it can contain.

Thus, bit_shifts.pc can have 20 as its max value.

So all that coverity OMG OMG sign-extension overflow above cannot actually
really happen, can it?

Because pc is promoted to an int, as the text rightfully points out.

Or am I way off here?

-- 
Regards/Gruss,
    Boris.

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