Development discussion of WireGuard
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From: Linus Torvalds <>
To: "Jason A. Donenfeld" <>
Subject: Random arrays on kernel stack..
Date: Thu, 28 Jul 2022 16:51:58 -0700	[thread overview]
Message-ID: <> (raw)

So I finally have an arm64 laptop that I'm playing with, and as a
result building the kernel the way I usually do - with warnings as

And I get this:

  drivers/net/wireguard/allowedips.c: In function ‘root_remove_peer_lists’:
  drivers/net/wireguard/allowedips.c:77:1: error: the frame size of
1040 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
     77 | }
        | ^
  drivers/net/wireguard/allowedips.c: In function ‘root_free_rcu’:
  drivers/net/wireguard/allowedips.c:64:1: error: the frame size of
1040 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
     64 | }
        | ^

and clearly it only happens for me because it turns out Asahi has for
some odd reason picked that low CONFIG_FRAME_WARN of just 1kB.

So the fix for the warning was just to update my .config file, no biggie.

But when I look at the code that generates that warning, it just
worries me. It has that magical constant 128.

Sure, that same constant is also in push_rcu().

And there it is randomly as a warning, and then it will happily
overflow the stack frame.

That's not ok.

I think that

 (a) that constant should be a bit lower, so that we *can* use a 1kB
stack frame warning on 64-bit architectures

 (b) it should be documented some way as a #define

 (c) push_rcu() should damn well not "warn and corrupt the stack". It
should warn-and-not-corrupt the stack, even if that then means that
the thing isn't pushed at all.



             reply	other threads:[~2022-07-28 23:52 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-07-28 23:51 Linus Torvalds [this message]
2022-07-29 17:12 ` Jason A. Donenfeld
2022-07-29 17:56   ` Linus Torvalds

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