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Message-ID: <20241107144156.GA2236807@yaz-khff2.amd.com>
Date: Thu, 7 Nov 2024 09:41:56 -0500
From: Yazen Ghannam <yazen.ghannam@....com>
To: Karan Sanghavi <karansanghvi98@...il.com>
Cc: Shuah Khan <skhan@...uxfoundation.org>, Tony Luck <tony.luck@...el.com>,
Borislav Petkov <bp@...en8.de>, linux-edac@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RAS/AMD/ATL: Fix unintended sign extension issue from
coverity
On Tue, Nov 05, 2024 at 04:20:27PM +0000, Karan Sanghavi wrote:
> On Mon, Nov 04, 2024 at 02:51:56PM -0700, Shuah Khan wrote:
> > On 11/4/24 11:34, Karan Sanghavi wrote:
> > > Explicit cast pc to u32 to avoid sign extension while left shift
> > >
> > > Issue reported by coverity with CID: 1593397
> > >
> > > Signed-off-by: Karan Sanghavi <karansanghvi98@...il.com>
> > > ---
> > > Coverity Link:
> > > https://scan7.scan.coverity.com/#/project-view/51975/11354?selectedIssue=1593397
> >
> > Please include the coverity message instead of this link so
> > reviewers without coverity accounts can see the report.
> >
> sure will keep it in mind.
Please do share this as it'll help provide context.
> > > ---
> > > drivers/ras/amd/atl/umc.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/ras/amd/atl/umc.c b/drivers/ras/amd/atl/umc.c
> > > index dc8aa12f63c8..916c867faaf8 100644
> > > --- a/drivers/ras/amd/atl/umc.c
> > > +++ b/drivers/ras/amd/atl/umc.c
> > > @@ -293,7 +293,7 @@ static unsigned long convert_dram_to_norm_addr_mi300(unsigned long addr)
> > > }
> > > /* PC bit */
> > > - addr |= pc << bit_shifts.pc;
> > > + addr |= (u32)pc << bit_shifts.pc;
> >
> > How did you determine this is the right fix and how did
> > test this change?
> >
> #define ADDR_SEL_2_CHAN GENMASK(15, 12)
>
> bit_shifts.pc = 5 + FIELD_GET(ADDR_SEL_2_CHAN, temp);
>
> After reviewing the code, I found that bit_shifts.pc can reach a maximum value of 20.
> Left-shifting a u16 pc by this amount results in an implicit promotion to an int64_t,
> which can cause sign extension and lead to unintended negative values.
>
The 'pc' variable holds a single bit in practice.
#define MI300_UMC_MCA_PC BIT(25)
pc = FIELD_GET(MI300_UMC_MCA_PC, addr);
> To avoid this, casting to a larger data type (such as u64) woulbe be most
> appropriate solution here.
>
> Also,using u64 would be more appropriate rather than u32.
>
> Should I send a new patch with u64?
>
Another option is to follow the style in the rest of the function and
use the 'temp' variable.
/* PC bit */
- addr |= pc << bit_shifts.pc;
+ temp = pc;
+ addr |= temp << bit_shifts.pc;
Or we can change the variable declarations to all be 'unsigned long' to
match input/return value.
Thanks,
Yazen
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