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Kernel: Assert that copy_to/from_user() are called with user addresses

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This will panic the kernel immediately if these functions are misused
so we can catch it and fix the misuse.

This patch fixes a couple of misuses:

    - create_signal_trampolines() writes to a user-accessible page
      above the 3GB address mark. We should really get rid of this
      page but that's a whole other thing.

    - CoW faults need to use copy_from_user rather than copy_to_user
      since it's the *source* pointer that points to user memory.

    - Inode faults need to use memcpy rather than copy_to_user since
      we're copying a kernel stack buffer into a quickmapped page.

This should make the copy_to/from_user() functions slightly less useful
for exploitation. Before this, they were essentially just glorified
memcpy() with SMAP disabled. :^)
This commit is contained in:
Andreas Kling
2020-01-19 09:14:14 +01:00
parent 2cd212e5df
commit f7b394e9a1
6 changed files with 33 additions and 15 deletions
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7
Kernel/Process.cpp
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@@ -1380,8 +1380,11 @@ void create_signal_trampolines()
u8* trampoline_end = (u8*)asm_signal_trampoline_end;
size_t trampoline_size = trampoline_end - trampoline;
u8* code_ptr = (u8*)trampoline_region->vaddr().as_ptr();
copy_to_user(code_ptr, trampoline, trampoline_size);
{
SmapDisabler disabler;
u8* code_ptr = (u8*)trampoline_region->vaddr().as_ptr();
memcpy(code_ptr, trampoline, trampoline_size);
}
trampoline_region->set_writable(false);
trampoline_region->remap();