From: Rick Lindsley ricklind@linux.vnet.ibm.com
commit f39356261c265a0689d7ee568132d516e8b6cecc upstream.
When the memset code was added to pgd_alloc(), it failed to consider that kmem_cache_alloc() can return NULL. It's uncommon, but not impossible under heavy memory contention. Example oops:
Unable to handle kernel paging request for data at address 0x00000000 Faulting instruction address: 0xc0000000000a4000 Oops: Kernel access of bad area, sig: 11 [#1] LE SMP NR_CPUS=2048 NUMA pSeries CPU: 70 PID: 48471 Comm: entrypoint.sh Kdump: loaded Not tainted 4.14.0-115.6.1.el7a.ppc64le #1 task: c000000334a00000 task.stack: c000000331c00000 NIP: c0000000000a4000 LR: c00000000012f43c CTR: 0000000000000020 REGS: c000000331c039c0 TRAP: 0300 Not tainted (4.14.0-115.6.1.el7a.ppc64le) MSR: 800000010280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE,TM[E]> CR: 44022840 XER: 20040000 CFAR: c000000000008874 DAR: 0000000000000000 DSISR: 42000000 SOFTE: 1 ... NIP [c0000000000a4000] memset+0x68/0x104 LR [c00000000012f43c] mm_init+0x27c/0x2f0 Call Trace: mm_init+0x260/0x2f0 (unreliable) copy_mm+0x11c/0x638 copy_process.isra.28.part.29+0x6fc/0x1080 _do_fork+0xdc/0x4c0 ppc_clone+0x8/0xc Instruction dump: 409e000c b0860000 38c60002 409d000c 90860000 38c60004 78a0d183 78a506a0 7c0903a6 41820034 60000000 60420000 <f8860000> f8860008 f8860010 f8860018
Fixes: fc5c2f4a55a2 ("powerpc/mm/hash64: Zero PGD pages on allocation") Cc: stable@vger.kernel.org # v4.16+ Signed-off-by: Rick Lindsley ricklind@vnet.linux.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/include/asm/book3s/64/pgalloc.h | 3 +++ 1 file changed, 3 insertions(+)
--- a/arch/powerpc/include/asm/book3s/64/pgalloc.h +++ b/arch/powerpc/include/asm/book3s/64/pgalloc.h @@ -83,6 +83,9 @@ static inline pgd_t *pgd_alloc(struct mm
pgd = kmem_cache_alloc(PGT_CACHE(PGD_INDEX_SIZE), pgtable_gfp_flags(mm, GFP_KERNEL)); + if (unlikely(!pgd)) + return pgd; + /* * Don't scan the PGD for pointers, it contains references to PUDs but * those references are not full pointers and so can't be recognised by