CVE-2023-54278

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

s390/vmem: split pages when debug pagealloc is enabled

Since commit bb1520d581a3 ("s390/mm: start kernel with DAT enabled") the kernel crashes early during boot when debug pagealloc is enabled:

mem auto-init: stack:off, heap alloc:off, heap free:off addressing exception: 0005 ilc:2 [#1] SMP DEBUG_PAGEALLOC Modules linked in: CPU: 0 PID: 0 Comm: swapper Not tainted 6.5.0-rc3-09759-gc5666c912155 #630 [..] Krnl Code: 00000000001325f6: ec5600248064 cgrj %r5,%r6,8,000000000013263e 00000000001325fc: eb880002000c srlg %r8,%r8,2 #0000000000132602: b2210051 ipte %r5,%r1,%r0,0

0000000000132606: b90400d1 lgr %r13,%r1 000000000013260a: 41605008 la %r6,8(%r5) 000000000013260e: a7db1000 aghi %r13,4096 0000000000132612: b221006d ipte %r6,%r13,%r0,0 0000000000132616: e3d0d0000171 lay %r13,4096(%r13)

Call Trace: _kernelmappages+0x14e/0x320 _freepagesok+0x23a/0x5a8) freelowmemorycoreearly+0x214/0x2c8 memblockfreeall+0x28/0x58 meminit+0xb6/0x228 mmcoreinit+0xb6/0x3b0 startkernel+0x1d2/0x5a8 startupcontinue+0x36/0x40 Kernel panic - not syncing: Fatal exception: panicon_oops

This is caused by using large mappings on machines with EDAT1/EDAT2. Add the code to split the mappings into 4k pages if debug pagealloc is enabled by CONFIGDEBUGPAGEALLOCENABLEDEFAULT or the debug_pagealloc kernel command line option.