On Thu, 16 Jun 2022 07:20:40 -0700, Dave Hansen wrote:
On 6/16/22 07:15, Yuntao Wang wrote:
On Thu, 16 Jun 2022 07:02:56 -0700, Dave Hansen wrote:
On 6/16/22 06:55, Yuntao Wang wrote:
There are two issues in phys_p4d_init():
The __kernel_physical_mapping_init() does not do boundary-checking for paddr_end and passes it directly to phys_p4d_init(), phys_p4d_init() does not do bounds checking either, so if the physical memory to be mapped is large enough, 'p4d_page + p4d_index(vaddr)' will wrap around to the beginning entry of the P4D table and its data will be overwritten.
The for loop body will be executed only when 'vaddr < vaddr_end' evaluates to true, but if that condition is true, 'paddr >= paddr_end' will evaluate to false, thus the 'if (paddr >= paddr_end) {}' block will never be executed and become dead code.
Could you explain a bit how you found this? Was this encountered in practice and debugged or was it found by inspection?
I found it by inspection.
Dare I ask how this was tested?
Due to some limitations, I didn't test the changes thoroughly, I just built the kernel and booted it in QEMU.
Considering that the patch was not fully tested, I spent a lot of time reviewing the code I changed and tried my best to make it correct.