ARM: 9359/1: flush: check if the folio is reserved for no-mapping addresses

In the Linux kernel, the following vulnerability has been resolved:

ARM: 9359/1: flush: check if the folio is reserved for no-mapping addresses

Since commit a4d5613c4dc6 ("arm: extend pfn_valid to take into account

freed memory map alignment") changes the semantics of pfn_valid() to check

presence of the memory map for a PFN. A valid page for an address which

is reserved but not mapped by the kernel[1], the system crashed during

some uio test with the following memory layout:

node 0: [mem 0x00000000c0a00000-0x00000000cc8fffff]

node 0: [mem 0x00000000d0000000-0x00000000da1fffff]

the uio layout is：0xc0900000, 0x100000

the crash backtrace like:

Unable to handle kernel paging request at virtual address bff00000

[...]

CPU: 1 PID: 465 Comm: startapp.bin Tainted: G O 5.10.0 #1

Hardware name: Generic DT based system

PC is at b15_flush_kern_dcache_area+0x24/0x3c

LR is at __sync_icache_dcache+0x6c/0x98

[...]

(b15_flush_kern_dcache_area) from (__sync_icache_dcache+0x6c/0x98)

(__sync_icache_dcache) from (set_pte_at+0x28/0x54)

(set_pte_at) from (remap_pfn_range+0x1a0/0x274)

(remap_pfn_range) from (uio_mmap+0x184/0x1b8 [uio])

(uio_mmap [uio]) from (__mmap_region+0x264/0x5f4)

(__mmap_region) from (__do_mmap_mm+0x3ec/0x440)

(__do_mmap_mm) from (do_mmap+0x50/0x58)

(do_mmap) from (vm_mmap_pgoff+0xfc/0x188)

(vm_mmap_pgoff) from (ksys_mmap_pgoff+0xac/0xc4)

(ksys_mmap_pgoff) from (ret_fast_syscall+0x0/0x5c)

Code: e0801001 e2423001 e1c00003 f57ff04f (ee070f3e)

---[ end trace 09cf0734c3805d52 ]---

Kernel panic - not syncing: Fatal exception

So check if PG_reserved was set to solve this issue.

[1]: https://lore.kernel.org/lkml/[email protected]/