mm: make apply_to_page_range more robust

PATCH Superseded Mika Penttilä 3 participants 3 messages Jan 20, 2016 – Jan 21, 2016

Subsystems (2)

Memory management MM core

lore

Share & tools

lore

Mika Penttilä

author

2016-01-20 05:17 UTC #0 lore raw

PATCH v2 1/1 mm: make apply_to_page_range more robust

Recent changes (4.4.0+) in module loader triggered oops on ARM.

can be 0 triggering the bug BUG_ON(addr >= end);.

The call path is SyS_init_module()->set_memory_xx()->apply_to_page_range(), and apply_to_page_range gets zero length resulting in triggering :

BUG_ON(addr >= end)

This is a consequence of changes in module section handling (Rusty CC:ed). This may be triggable only with certain modules and/or gcc versions.

Plus, I think the spirit of the BUG_ON is to catch overflows, not to bug on zero length legitimate callers. So whatever the reason for this triggering, some day we have another caller with zero length.

Fix by letting call with zero size succeed.

v2: add more explanation

Signed-off-by Mika PenttilA? [email protected]

Reviewed-by Pekka Enberg <[email protected]>

---

mm/memory.c +3 -0

index c387430..c3d1a2e 100644
@@ -1884,6 +1884,9 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
        unsigned long end = addr + size;
        int err;
 
+       if (!size)
+               return 0;
+
        BUG_ON(addr >= end);
        pgd = pgd_offset(mm, addr);
        do {

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>

David Rientjes

2016-01-20 23:37 UTC #1 lore raw

Quoted 4 lines · Mika PenttilA?

Recent changes (4.4.0+) in module loader triggered oops on ARM.
can be 0 triggering the bug BUG_ON(addr >= end);.

Quoted 8 lines

The call path is SyS_init_module()->set_memory_xx()->apply_to_page_range(), and apply_to_page_range gets zero length resulting in triggering :
BUG_ON(addr >= end)
This is a consequence of changes in module section handling (Rusty CC:ed). This may be triggable only with certain modules and/or gcc versions.

Well, what module are you loading to cause this crash? Why would it be passing size == 0 to apply_to_page_range()? Again, that sounds like a problem that we _want_ to know about since it is probably the result of buggy code and this patch would be covering it up.

Please elaborate on the problem that you are seeing, preferably with a stack trace of the BUG so we can fix the problem instead of papering over it.

Rusty Russell

2016-01-21 05:11 UTC #2 lore raw

Quoted 11 lines · David Rientjes

Quoted 9 lines · Mika Penttilä
Recent changes (4.4.0+) in module loader triggered oops on ARM.
can be 0 triggering the bug BUG_ON(addr >= end);.
The call path is SyS_init_module()->set_memory_xx()->apply_to_page_range(), and apply_to_page_range gets zero length resulting in triggering :
BUG_ON(addr >= end)

Quoted 8 lines

Quoted 3 lines
This is a consequence of changes in module section handling (Rusty CC:ed). This may be triggable only with certain modules and/or gcc versions.
Well, what module are you loading to cause this crash? Why would it be passing size == 0 to apply_to_page_range()? Again, that sounds like a problem that we _want_ to know about since it is probably the result of buggy code and this patch would be covering it up.

Yes, I'm curious too. It's certainly possible, since I expected a zero-length range to do nothing, but let's make sure we're not papering over some other screwup of mine.

Thanks,
Rusty.