linux-kernel - Re: [syzbot] [bpf?] WARNING in reg_bounds_sanity

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Message-ID: <c794309d89d0ffb49d891d7b600831abbfa4dc65.camel@gmail.com>
Date: Fri, 04 Jul 2025 14:27:58 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Paul Chaignon <paul.chaignon@...il.com>
Cc: syzbot <syzbot+c711ce17dd78e5d4fdcf@...kaller.appspotmail.com>, 
	andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
 daniel@...earbox.net, 	haoluo@...gle.com, john.fastabend@...il.com,
 jolsa@...nel.org, kpsingh@...nel.org, 	linux-kernel@...r.kernel.org,
 martin.lau@...ux.dev, netdev@...r.kernel.org, 	sdf@...ichev.me,
 song@...nel.org, syzkaller-bugs@...glegroups.com, 	yonghong.song@...ux.dev
Subject: Re: [syzbot] [bpf?] WARNING in reg_bounds_sanity_check

On Fri, 2025-07-04 at 14:13 -0700, Eduard Zingerman wrote:

[...]

> I think the mask can be computed as in or_range() function at the
> bottom of the email. This gives the following algorithm, if only
> unsigned range is considered:
> 
> - assume prediction is needed for "if a & b goto ..."
> - bits that may be set in 'a' are or_range(a_min, a_max)
> - bits that may be set in 'b' are or_range(b_min, b_max)
> - if computed bit masks intersect: both branches are possible
> - otherwise only false branch is possible.
> 
> Wdyt?

This does not help with problem at hand, however.
Possible bits set for range [0x1, 0xff] are 0xff,
so there would be no prediction.