On Sat, 18 Jun 2022 03:22:20 +0300, Kirill A. Shutemov wrote:
On Thu, Jun 16, 2022 at 09:55:10PM +0800, 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.
To fix these issues, use 'i < PTRS_PER_P4D' instead of 'vaddr < vaddr_end' as the for loop condition, this also make it more consistent with the logic of the phys_{pud,pmt,pte}_init() functions.
Hm. I don't see why you changed phys_p4d_init(), but not __kernel_physical_mapping_init(). It does exactly the same thing, just pgd_index() is hidden a bit deeper than p4d_index().
The reason I chose to change phys_p4d_init() is that:
- Currently the 'if (paddr >= paddr_end) {}' block in phys_p4d_init() is dead code, changing __kernel_physical_mapping_init() does not fix that.
- Changing phys_p4d_init() to the 'for (i < PTRS_PER_P4D) {}' form makes it more consistent with phys_pud/pmt/pte_init() as they are all using the 'for (i < PTRS_PER_PUD/PMD/PTE) {}' forms. Meanwhile, this change also fixes the dead code issue.
thanks,
Yuntao Wang