Commit 360cb4d1 authored Jul 14, 2016 by Andy Lutomirski Committed by Ingo Molnar Jul 15, 2016

x86/mm/cpa: In populate_pgd(), don't set the PGD entry until it's populated



This avoids pointless races in which another CPU or task might see a
partially populated global PGD entry.  These races should normally
be harmless, but, if another CPU propagates the entry via
vmalloc_fault() and then populate_pgd() fails (due to memory allocation
failure, for example), this prevents a use-after-free of the PGD
entry.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/bf99df27eac6835f687005364bd1fbd89130946c.1468527351.git.luto@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent af2cf278

arch/x86/mm/pageattr.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -1104,8 +1104,6 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
		pud = (pud_t *)get_zeroed_page(GFP_KERNEL \| __GFP_NOTRACK);
		if (!pud)
		return -1;

		set_pgd(pgd_entry, __pgd(__pa(pud) \| _KERNPG_TABLE));
		}

		pgprot_val(pgprot) &= ~pgprot_val(cpa->mask_clr);
		@@ -1113,11 +1111,16 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)

		ret = populate_pud(cpa, addr, pgd_entry, pgprot);
		if (ret < 0) {
		unmap_pgd_range(cpa->pgd, addr,
		if (pud)
		free_page((unsigned long)pud);
		unmap_pud_range(pgd_entry, addr,
		addr + (cpa->numpages << PAGE_SHIFT));
		return ret;
		}

		if (pud)
		set_pgd(pgd_entry, __pgd(__pa(pud) \| _KERNPG_TABLE));

		cpa->numpages = ret;
		return 0;
		}