x86/mm/cpa: In populate_pgd(), don't set the PGD entry until it's populated (360cb4d1) · Commits · 戴 / test

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>

arch/x86/mm/pageattr.c

+6 −3

Original line number	Original line	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);		pud = (pud_t *)get_zeroed_page(GFP_KERNEL \| __GFP_NOTRACK);
	if (!pud)		if (!pud)
	return -1;		return -1;

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

	pgprot_val(pgprot) &= ~pgprot_val(cpa->mask_clr);		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);		ret = populate_pud(cpa, addr, pgd_entry, pgprot);
	if (ret < 0) {		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));		addr + (cpa->numpages << PAGE_SHIFT));
	return ret;		return ret;
	}		}

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

	cpa->numpages = ret;		cpa->numpages = ret;
	return 0;		return 0;
	}		}

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