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Kernel: Stop perf event stack walk on bogus userspace->kernel traversal

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When walking the stack to generate a perf_event sample, we now check
if a userspace stack frame points back into kernel memory.

It was possible to use this as an arbitrary kernel memory read. :^)
This commit is contained in:
Andreas Kling 2021-12-19 16:38:46 +01:00
parent d82c91ac2c
commit 8ef9b003ad
1 changed files with 11 additions and 0 deletions
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11
Kernel/PerformanceEventBuffer.cpp
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@ -43,10 +43,21 @@ static Vector<FlatPtr, PerformanceEvent::max_stack_frame_count> raw_backtrace(Fl
FlatPtr stack_ptr = bp; FlatPtr stack_ptr = bp;
// FIXME: Figure out how to remove this SmapDisabler without breaking profile stacks. // FIXME: Figure out how to remove this SmapDisabler without breaking profile stacks.
SmapDisabler disabler; SmapDisabler disabler;
// NOTE: The stack should always have kernel frames first, followed by userspace frames.
// If a userspace frame points back into kernel memory, something is afoot.
bool is_walking_userspace_stack = false;
while (stack_ptr) { while (stack_ptr) {
void* fault_at; void* fault_at;
if (!safe_memcpy(&stack_ptr_copy, (void*)stack_ptr, sizeof(FlatPtr), fault_at)) if (!safe_memcpy(&stack_ptr_copy, (void*)stack_ptr, sizeof(FlatPtr), fault_at))
break; break;
if (!Memory::is_user_address(VirtualAddress { stack_ptr })) {
if (is_walking_userspace_stack) {
dbgln("SHENANIGANS! Userspace stack points back into kernel memory");
break;
}
} else {
is_walking_userspace_stack = true;
}
FlatPtr retaddr; FlatPtr retaddr;
if (!safe_memcpy(&retaddr, (void*)(stack_ptr + sizeof(FlatPtr)), sizeof(FlatPtr), fault_at)) if (!safe_memcpy(&retaddr, (void*)(stack_ptr + sizeof(FlatPtr)), sizeof(FlatPtr), fault_at))
break; break;