linux-kernel - Re: [PATCH] iommu: Fix shift-out-of-bounds in iova_bitmap_offset_to

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Message-ID: <20250113162230.GH26854@ziepe.ca>
Date: Mon, 13 Jan 2025 12:22:30 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Joao Martins <joao.m.martins@...cle.com>
Cc: Qasim Ijaz <qasdev00@...il.com>, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, Kevin Tian <kevin.tian@...el.com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH] iommu: Fix shift-out-of-bounds in
 iova_bitmap_offset_to_index()

On Mon, Jan 13, 2025 at 12:00:29PM +0000, Joao Martins wrote:
> On 12/01/2025 12:39, Qasim Ijaz wrote:
> > This patch resolves a UBSAN shift-out-of-bounds issue in 
> 
> Avoid the 'this patch' e.g. Resolve a UBSAN shift-out-of-bonds (...)
> 
> The Subject component part could also be a bit more specific e.g.
> 
> iommufd/iova_bitmap: Fix shift-out-of-bounds in iova_bitmap_offset_to_index()
> 
> > iova_bitmap_offset_to_index() where shifting the constant "1" (of type int) 
> > by bitmap->mapped.pgshift (an unsigned long value) could result in undefined behavior. 
> > 
> > The constant "1" defaults to a 32-bit "int", and when "pgshift" exceeds 31 (e.g., pgshift = 63)
> > the shift operation overflows, as the result cannot be represented in a 32-bit type.
> > 
> > To resolve this, the constant is updated to "1UL", promoting it to an unsigned long type 
> > to match the operand's type.
> > 
> > Reported-by: syzbot <syzbot+85992ace37d5b7b51635@...kaller.appspotmail.com>
> > Closes: https://syzkaller.appspot.com/bug?extid=85992ace37d5b7b51635
> > Signed-off-by: Qasim Ijaz <qasdev00@...il.com>
> 
> With those two nits:
> 
> 	Reviewed-by: Joao Martins <joao.m.martins@...cle.com>

It needs a fixes line too

Jason