Re: [PATCH] usercopy: Do not fail on memory from former init sections

Re: [PATCH] usercopy: Do not fail on memory from former init sections

[Andrew Morton]

On Fri, 7 Jan 2022 01:19:24 +0100 Helge Deller <deller@gmx.de> wrote:

> On some platforms the memory area between the _stext and the _etext
> symbols includes the init sections (parisc and csky). If the init
> sections are freed after bootup, the kernel may reuse this memory.
> 
> In one test the usercopy checks if the given address is inside the .text
> section (from _stext to _etext), and it wrongly fails on the mentioned
> platforms if the memory is from the former init section.
> 
> Fix this failure by first checking against the init sections before
> checking against the _stext/_etext section.

This sounds like it might have very serious runtime effects?

Please always fully describe a bug's runtime effects when fixing that bug.

> Fixes: 98400ad75e95 ("parisc: Fix backtrace to always include init funtion names")

So is this a must-have for 5.16?

Re: [PATCH] usercopy: Do not fail on memory from former init sections

[Andrew Morton]

On Fri, 7 Jan 2022 01:19:24 +0100 Helge Deller <deller@gmx.de> wrote:

> On some platforms the memory area between the _stext and the _etext
> symbols includes the init sections (parisc and csky). If the init
> sections are freed after bootup, the kernel may reuse this memory.
> 
> In one test the usercopy checks if the given address is inside the .text
> section (from _stext to _etext), and it wrongly fails on the mentioned
> platforms if the memory is from the former init section.
> 
> Fix this failure by first checking against the init sections before
> checking against the _stext/_etext section.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> Fixes: 98400ad75e95 ("parisc: Fix backtrace to always include init funtion names")
> 

And 98400ad75e95 has cc:stable so we'll want cc:stable on this patch
also, yes?

Re: [PATCH] usercopy: Do not fail on memory from former init sections

[Andrew Morton]

On Fri, 7 Jan 2022 01:19:24 +0100 Helge Deller <deller@gmx.de> wrote:

> On some platforms the memory area between the _stext and the _etext
> symbols includes the init sections (parisc and csky). If the init
> sections are freed after bootup, the kernel may reuse this memory.
> 
> In one test the usercopy checks if the given address is inside the .text
> section (from _stext to _etext), and it wrongly fails on the mentioned
> platforms if the memory is from the former init section.
> 
> Fix this failure by first checking against the init sections before
> checking against the _stext/_etext section.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> Fixes: 98400ad75e95 ("parisc: Fix backtrace to always include init funtion names")

Wait.  98400ad75e95 is actually called

	Revert "parisc: Fix backtrace to always include init funtion names"

and it reverts 279917e27edc2.  This isn't making a lot of sense.


And neither 98400ad75e95 nor 279917e27edc2 touch csky.

And I really wouldn't want to jam a patch into mm/usercopy.c at this
point in the life of 5.16 anyway.

I'll drop this patch.  Please revisit and clarify all these things.  A lot!