Extables#220
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wipawel
previously approved these changes
Oct 15, 2021
| { | ||
| __start_extables = .; | ||
| *(.extables) | ||
| __stop_extables = .; |
| #include <mm/regions.h> | ||
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| void init_extables(void) { | ||
| for (extable_entry_t *cur = __start_extables; cur < __stop_extables; ++cur) { |
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Good idea to have them sanity checked. Thanks!
Next step could be to sort them and use bsearch to speed up lookup.
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Right now we've only like 8 entries, so a linear search should still be fast enough. ;) But yeah, when we get more users and especially ones in hot code, speeding up the search might make sense.
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| use_extables(regs); | ||
| if (extables_fixup(regs)) | ||
| return; |
82marbag
previously approved these changes
Oct 15, 2021
Change the type of the __{start,end}_* markers to unsigned char so
pointer diff does "The Right Thing"™, i.e. give the byte difference,
not the object count difference.
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
The extables handling is broken as in not being able to handle exceptions gracefully. They'll all end up in a panic, which is probably not intended. Make use_extables() return a boolean that tells if the exception was handled or not. If it was, we can simply return from the exception handler and continue execution. Also don't support doing both, a fixup IP and a callback. Only do one and prefer the fixup IP which is currently the only use case. Last, but not least, use the oppurtunity to rename the function to extables_fixup(), as that's what it does: fixing up the exception. Signed-off-by: Mathias Krause <minipli@grsecurity.net>
We round up the extables array to a multiple of 4kB. However, this leads to empty extable entries, i.e. entries for NULL ptr faults without a fixup IP nor a callback. To avoid bogus handling of these, introduce a new symbol __stop_extables[] that points to the end of legitimate extable entries. Leave __end_extables[] as is to lower the amount of code churn. However, change its type to unsigned char to avoid and flag accidental misuse. Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Some headers lack explicit includes for #defines / types they use. Add these to avoid these implicit include dependencies. Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Ensure all entries have a fixup IP or a callback. Panic if an entry lacks both. Signed-off-by: Mathias Krause <minipli@grsecurity.net>
auto-merge was automatically disabled
October 15, 2021 14:25
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82marbag
approved these changes
Oct 15, 2021
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This PR fixes the extable handling as in not triggering a panic or handling NULL pointer dereferences in an endless loop. E.g. when booting on a VM with too little memory we'll now fail gracefully instead of looping in exception handling:
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