Re: [RFC] mm/pgtable/debug: Add test validating architecture page table helpers

[Russell King - ARM Linux admin]

On Thu, Jul 25, 2019 at 12:25:23PM +0530, Anshuman Khandual wrote:
> This adds a test module which will validate architecture page table helpers
> and accessors regarding compliance with generic MM semantics expectations.
> This will help various architectures in validating changes to the existing
> page table helpers or addition of new ones.
> 
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Mark Brown <Mark.Brown@xxxxxxx>
> Cc: Steven Price <Steven.Price@xxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Sri Krishna chowdary <schowdary@xxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: x86@xxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> 
> Suggested-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
>  lib/Kconfig.debug       |  14 +++
>  lib/Makefile            |   1 +
>  lib/test_arch_pgtable.c | 290 ++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 305 insertions(+)
>  create mode 100644 lib/test_arch_pgtable.c
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5960e29..a27fe8d 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1719,6 +1719,20 @@ config TEST_SORT
>  
>  	  If unsure, say N.
>  
> +config TEST_ARCH_PGTABLE
> +	tristate "Test arch page table helpers for semantics compliance"
> +	depends on MMU
> +	depends on DEBUG_KERNEL || m
> +	help
> +	  This options provides a kernel module which can be used to test
> +	  architecture page table helper functions on various platform in
> +	  verifing if they comply with expected generic MM semantics. This
> +	  will help architectures code in making sure that any changes or
> +	  new additions of these helpers will still conform to generic MM
> +	  expeted semantics.
> +
> +	  If unsure, say N.
> +
>  config KPROBES_SANITY_TEST
>  	bool "Kprobes sanity tests"
>  	depends on DEBUG_KERNEL
> diff --git a/lib/Makefile b/lib/Makefile
> index 095601c..0806d61 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -76,6 +76,7 @@ obj-$(CONFIG_TEST_VMALLOC) += test_vmalloc.o
>  obj-$(CONFIG_TEST_OVERFLOW) += test_overflow.o
>  obj-$(CONFIG_TEST_RHASHTABLE) += test_rhashtable.o
>  obj-$(CONFIG_TEST_SORT) += test_sort.o
> +obj-$(CONFIG_TEST_ARCH_PGTABLE) += test_arch_pgtable.o
>  obj-$(CONFIG_TEST_USER_COPY) += test_user_copy.o
>  obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_keys.o
>  obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_key_base.o
> diff --git a/lib/test_arch_pgtable.c b/lib/test_arch_pgtable.c
> new file mode 100644
> index 0000000..1396664
> --- /dev/null
> +++ b/lib/test_arch_pgtable.c
> @@ -0,0 +1,290 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * This kernel module validates architecture page table helpers &
> + * accessors and helps in verifying their continued compliance with
> + * generic MM semantics.
> + *
> + * Copyright (C) 2019 ARM Ltd.
> + *
> + * Author: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> + */
> +#define pr_fmt(fmt) "test_arch_pgtable: %s " fmt, __func__
> +
> +#include <linux/kernel.h>
> +#include <linux/hugetlb.h>
> +#include <linux/mm.h>
> +#include <linux/mman.h>
> +#include <linux/mm_types.h>
> +#include <linux/module.h>
> +#include <linux/printk.h>
> +#include <linux/swap.h>
> +#include <linux/swapops.h>
> +#include <linux/pfn_t.h>
> +#include <linux/gfp.h>
> +#include <asm/pgalloc.h>
> +#include <asm/pgtable.h>
> +
> +/*
> + * Basic operations
> + *
> + * mkold(entry)			= An old and not an young entry
> + * mkyoung(entry)		= An young and not an old entry
> + * mkdirty(entry)		= A dirty and not a clean entry
> + * mkclean(entry)		= A clean and not a dirty entry
> + * mkwrite(entry)		= An write and not an write protected entry
> + * wrprotect(entry)		= An write protected and not an write entry
> + * pxx_bad(entry)		= A mapped and non-table entry
> + * pxx_same(entry1, entry2)	= Both entries hold the exact same value
> + */
> +#define VMA_TEST_FLAGS (VM_READ|VM_WRITE|VM_EXEC)
> +
> +static struct vm_area_struct vma;
> +static struct mm_struct mm;
> +static struct page *page;
> +static pgprot_t prot;
> +static unsigned long pfn, addr;
> +
> +static void pte_basic_tests(void)
> +{
> +	pte_t pte;
> +
> +	pte = mk_pte(page, prot);
> +	WARN_ON(!pte_same(pte, pte));
> +	WARN_ON(!pte_young(pte_mkyoung(pte)));
> +	WARN_ON(!pte_dirty(pte_mkdirty(pte)));
> +	WARN_ON(!pte_write(pte_mkwrite(pte)));
> +	WARN_ON(pte_young(pte_mkold(pte)));
> +	WARN_ON(pte_dirty(pte_mkclean(pte)));
> +	WARN_ON(pte_write(pte_wrprotect(pte)));
> +}
> +
> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE
> +static void pmd_basic_tests(void)
> +{
> +	pmd_t pmd;
> +
> +	pmd = mk_pmd(page, prot);

mk_pmd() is provided on 32-bit ARM LPAE, which also sets
HAVE_ARCH_TRANSPARENT_HUGEPAGE, so this should be fine.

> +	WARN_ON(!pmd_same(pmd, pmd));
> +	WARN_ON(!pmd_young(pmd_mkyoung(pmd)));
> +	WARN_ON(!pmd_dirty(pmd_mkdirty(pmd)));
> +	WARN_ON(!pmd_write(pmd_mkwrite(pmd)));
> +	WARN_ON(pmd_young(pmd_mkold(pmd)));
> +	WARN_ON(pmd_dirty(pmd_mkclean(pmd)));
> +	WARN_ON(pmd_write(pmd_wrprotect(pmd)));
> +	/*
> +	 * A huge page does not point to next level page table
> +	 * entry. Hence this must qualify as pmd_bad().
> +	 */
> +	WARN_ON(!pmd_bad(pmd_mkhuge(pmd)));
> +}
> +#else
> +static void pmd_basic_tests(void) { }
> +#endif
> +
> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> +static void pud_basic_tests(void)
> +{
> +	pud_t pud;
> +
> +	pud = pfn_pud(pfn, prot);
> +	WARN_ON(!pud_same(pud, pud));
> +	WARN_ON(!pud_young(pud_mkyoung(pud)));
> +	WARN_ON(!pud_write(pud_mkwrite(pud)));
> +	WARN_ON(pud_write(pud_wrprotect(pud)));
> +	WARN_ON(pud_young(pud_mkold(pud)));
> +
> +#if !defined(__PAGETABLE_PMD_FOLDED) && !defined(__ARCH_HAS_4LEVEL_HACK)
> +	/*
> +	 * A huge page does not point to next level page table
> +	 * entry. Hence this must qualify as pud_bad().
> +	 */
> +	WARN_ON(!pud_bad(pud_mkhuge(pud)));
> +#endif
> +}
> +#else
> +static void pud_basic_tests(void) { }
> +#endif
> +
> +static void p4d_basic_tests(void)
> +{
> +	pte_t pte;
> +	p4d_t p4d;
> +
> +	pte = mk_pte(page, prot);
> +	p4d = (p4d_t) { (pte_val(pte)) };
> +	WARN_ON(!p4d_same(p4d, p4d));

If the intention is to test p4d_same(), is this really a sufficient test?

> +}
> +
> +static void pgd_basic_tests(void)
> +{
> +	pte_t pte;
> +	pgd_t pgd;
> +
> +	pte = mk_pte(page, prot);
> +	pgd = (pgd_t) { (pte_val(pte)) };
> +	WARN_ON(!pgd_same(pgd, pgd));

If the intention is to test pgd_same(), is this really a sufficient test?

> +}
> +
> +#if !defined(__PAGETABLE_PMD_FOLDED) && !defined(__ARCH_HAS_4LEVEL_HACK)
> +static void pud_clear_tests(void)
> +{
> +	pud_t pud;
> +
> +	pud_clear(&pud);
> +	WARN_ON(!pud_none(pud));
> +}
> +
> +static void pud_populate_tests(void)
> +{
> +	pmd_t pmd;
> +	pud_t pud;
> +
> +	/*
> +	 * This entry points to next level page table page.
> +	 * Hence this must not qualify as pud_bad().
> +	 */
> +	pmd_clear(&pmd);

32-bit ARM sets __PAGETABLE_PMD_FOLDED so this is not a concern.

> +	pud_clear(&pud);
> +	pud_populate(&mm, &pud, &pmd);
> +	WARN_ON(pud_bad(pud));
> +}
> +#else
> +static void pud_clear_tests(void) { }
> +static void pud_populate_tests(void) { }
> +#endif
> +
> +#if !defined(__PAGETABLE_PUD_FOLDED) && !defined(__ARCH_HAS_5LEVEL_HACK)
> +static void p4d_clear_tests(void)
> +{
> +	p4d_t p4d;
> +
> +	p4d_clear(&p4d);
> +	WARN_ON(!p4d_none(p4d));
> +}
> +
> +static void p4d_populate_tests(void)
> +{
> +	pud_t pud;
> +	p4d_t p4d;
> +
> +	/*
> +	 * This entry points to next level page table page.
> +	 * Hence this must not qualify as p4d_bad().
> +	 */
> +	pud_clear(&pud);
> +	p4d_clear(&p4d);
> +	p4d_populate(&mm, &p4d, &pud);
> +	WARN_ON(p4d_bad(p4d));
> +}
> +#else
> +static void p4d_clear_tests(void) { }
> +static void p4d_populate_tests(void) { }
> +#endif
> +
> +#ifndef __PAGETABLE_P4D_FOLDED
> +static void pgd_clear_tests(void)
> +{
> +	pgd_t pgd;
> +
> +	pgd_clear(&pgd);
> +	WARN_ON(!pgd_none(pgd));
> +}
> +
> +static void pgd_populate_tests(void)
> +{
> +	pgd_t p4d;
> +	pgd_t pgd;
> +
> +	/*
> +	 * This entry points to next level page table page.
> +	 * Hence this must not qualify as pgd_bad().
> +	 */
> +	p4d_clear(&p4d);
> +	pgd_clear(&pgd);
> +	pgd_populate(&mm, &pgd, &p4d);
> +	WARN_ON(pgd_bad(pgd));
> +}
> +#else
> +static void pgd_clear_tests(void) { }
> +static void pgd_populate_tests(void) { }
> +#endif
> +
> +static void pxx_clear_tests(void)
> +{
> +	pte_t pte;
> +	pmd_t pmd;
> +
> +	pte_clear(NULL, 0, &pte);
> +	WARN_ON(!pte_none(pte));
> +
> +	pmd_clear(&pmd);

This really isn't going to be happy on 32-bit non-LPAE ARM.  Here, a
PMD is a 32-bit entry which is expected to be _within_ a proper PGD,
where a PGD is 16K in size, consisting of pairs of PMDs.

So, pmd_clear() expects to always be called for an _even_ PMD of the
pair, and will write to the even and following odd PMD.  Hence, the
above will scribble over the stack of this function.

> +	WARN_ON(!pmd_none(pmd));
> +
> +	pud_clear_tests();
> +	p4d_clear_tests();
> +	pgd_clear_tests();
> +}
> +
> +static void pxx_populate_tests(void)
> +{
> +	pmd_t pmd;
> +
> +	/*
> +	 * This entry points to next level page table page.
> +	 * Hence this must not qualify as pmd_bad().
> +	 */
> +	memset(page, 0, sizeof(*page));
> +	pmd_clear(&pmd);

This really isn't going to be happy on 32-bit non-LPAE ARM.  Here, a
PMD is a 32-bit entry which is expected to be _within_ a proper PGD,
where a PGD is 16K in size, consisting of pairs of PMDs.

So, pmd_clear() expects to always be called for an _even_ PMD of the
pair, and will write to the even and following odd PMD.  Hence, the
above will scribble over the stack of this function.

> +	pmd_populate(&mm, &pmd, page);

This too has the same expectations on 32-bit non-LPAE ARM.

> +	WARN_ON(pmd_bad(pmd));
> +
> +	pud_populate_tests();
> +	p4d_populate_tests();
> +	pgd_populate_tests();
> +}
> +
> +static int variables_alloc(void)
> +{
> +	vma_init(&vma, &mm);
> +	prot = vm_get_page_prot(VMA_TEST_FLAGS);
> +	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
> +	if (!page) {
> +		pr_err("Test struct page allocation failed\n");
> +		return 1;
> +	}
> +	pfn = page_to_pfn(page);
> +	addr = 0;
> +	return 0;
> +}
> +
> +static void variables_free(void)
> +{
> +	free_page((unsigned long)page_address(page));
> +}
> +
> +static int __init arch_pgtable_tests_init(void)
> +{
> +	int ret;
> +
> +	ret = variables_alloc();
> +	if (ret) {
> +		pr_err("Test resource initialization failed\n");
> +		return 1;
> +	}
> +
> +	pte_basic_tests();
> +	pmd_basic_tests();
> +	pud_basic_tests();
> +	p4d_basic_tests();
> +	pgd_basic_tests();
> +	pxx_clear_tests();
> +	pxx_populate_tests();
> +	variables_free();
> +	return 0;
> +}
> +
> +static void __exit arch_pgtable_tests_exit(void) { }
> +
> +module_init(arch_pgtable_tests_init);
> +module_exit(arch_pgtable_tests_exit);
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.7.4
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up