nios2: ensure that memblock.current_limit is set when setting pfn limits

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nios2: ensure that memblock.current_limit is set when setting pfn limits On nios2, with CONFIG_FLATMEM set, the kernel relies on memblock_get_current_limit() to determine the limits of mem_map, in particular for max_low_pfn. Unfortunately, memblock.current_limit is only default initialized to MEMBLOCK_ALLOC_ANYWHERE at this point of the bootup, potentially leading to situations where max_low_pfn can erroneously exceed the value of max_pfn and, thus, the valid range of available DRAM. This can in turn cause kernel-level paging failures, e.g.: [ 76.900000] Unable to handle kernel paging request at virtual address 20303000 [ 76.900000] ea = c0080890, ra = c000462c, cause = 14 [ 76.900000] Kernel panic - not syncing: Oops [ 76.900000] ---[ end Kernel panic - not syncing: Oops ]--- This patch fixes this by pre-calculating memblock.current_limit based on the upper limits of the available memory ranges via adjust_lowmem_bounds, a simplified version of the equivalent implementation within the arm architecture.

References

• https://git.kernel.org/stable/c/25f09699edd360b534ccae16bc276c3b52c471f3
• https://git.kernel.org/stable/c/5c3e38a367822f036227dd52bac82dc4a05157e2
• https://git.kernel.org/stable/c/b1ec9faef7e36269ca3ec890972a78effbaeb975
• https://git.kernel.org/stable/c/90f5f715550e07cd6a51f80fc3f062d832c8c997
• https://git.kernel.org/stable/c/8912814f14e298b83df072fecc1f7ed1b63b1b2c
• https://git.kernel.org/stable/c/a20b83cf45be2057f3d073506779e52c7fa17f94