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From:   Daniel Axtens <dja@axtens.net>
To:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>, kasan-dev@googlegroups.com,
        Qian Cai <cai@lca.pw>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Ryabinin <aryabinin@virtuozzo.com>
Subject: Re: [PATCH 2/2] kasan: Don't allocate page tables in kasan_release_vmalloc()
In-Reply-To: <20191204204534.32202-2-aryabinin@virtuozzo.com>
References: <20191204204534.32202-1-aryabinin@virtuozzo.com> <20191204204534.32202-2-aryabinin@virtuozzo.com>
Date:   Thu, 05 Dec 2019 10:28:18 +1100
Message-ID: <87eexjekml.fsf@dja-thinkpad.axtens.net>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Andrey Ryabinin <aryabinin@virtuozzo.com> writes:

Ah you beat me by a few hours, I was going to send a similar but
slightly simpler patch - we should be able to use apply_to_page_range
for the 'inner' part of the range and just walk the page table for the
possible pages on the edges of the range. That means we could avoid a
full, loop-driven page table walker. But I'd also be very open to
generalising apply_to_page_range(); I think I'd add
apply_to_existing_pages() and add an argument to the static walker
functions.

Let me try that out and we'll see what it looks like.

Regards,
Daniel

> The purpose of kasan_release_vmalloc() is to unmap and deallocate shadow
> memory. The usage of apply_to_page_range() isn't suitable in that scenario
> because it allocates pages to fill missing page tables entries.
> This also cause sleep in atomic bug:
>
> 	BUG: sleeping function called from invalid context at mm/page_alloc.c:4681
> 	in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 15087, name:
>
> 	Call Trace:
> 	 __dump_stack lib/dump_stack.c:77 [inline]
> 	 dump_stack+0x199/0x216 lib/dump_stack.c:118
> 	 ___might_sleep.cold.97+0x1f5/0x238 kernel/sched/core.c:6800
> 	 __might_sleep+0x95/0x190 kernel/sched/core.c:6753
> 	 prepare_alloc_pages mm/page_alloc.c:4681 [inline]
> 	 __alloc_pages_nodemask+0x3cd/0x890 mm/page_alloc.c:4730
> 	 alloc_pages_current+0x10c/0x210 mm/mempolicy.c:2211
> 	 alloc_pages include/linux/gfp.h:532 [inline]
> 	 __get_free_pages+0xc/0x40 mm/page_alloc.c:4786
> 	 __pte_alloc_one_kernel include/asm-generic/pgalloc.h:21 [inline]
> 	 pte_alloc_one_kernel include/asm-generic/pgalloc.h:33 [inline]
> 	 __pte_alloc_kernel+0x1d/0x200 mm/memory.c:459
> 	 apply_to_pte_range mm/memory.c:2031 [inline]
> 	 apply_to_pmd_range mm/memory.c:2068 [inline]
> 	 apply_to_pud_range mm/memory.c:2088 [inline]
> 	 apply_to_p4d_range mm/memory.c:2108 [inline]
> 	 apply_to_page_range+0x77d/0xa00 mm/memory.c:2133
> 	 kasan_release_vmalloc+0xa7/0xc0 mm/kasan/common.c:970
> 	 __purge_vmap_area_lazy+0xcbb/0x1f30 mm/vmalloc.c:1313
> 	 try_purge_vmap_area_lazy mm/vmalloc.c:1332 [inline]
> 	 free_vmap_area_noflush+0x2ca/0x390 mm/vmalloc.c:1368
> 	 free_unmap_vmap_area mm/vmalloc.c:1381 [inline]
> 	 remove_vm_area+0x1cc/0x230 mm/vmalloc.c:2209
> 	 vm_remove_mappings mm/vmalloc.c:2236 [inline]
> 	 __vunmap+0x223/0xa20 mm/vmalloc.c:2299
> 	 __vfree+0x3f/0xd0 mm/vmalloc.c:2356
> 	 __vmalloc_area_node mm/vmalloc.c:2507 [inline]
> 	 __vmalloc_node_range+0x5d5/0x810 mm/vmalloc.c:2547
> 	 __vmalloc_node mm/vmalloc.c:2607 [inline]
> 	 __vmalloc_node_flags mm/vmalloc.c:2621 [inline]
> 	 vzalloc+0x6f/0x80 mm/vmalloc.c:2666
> 	 alloc_one_pg_vec_page net/packet/af_packet.c:4233 [inline]
> 	 alloc_pg_vec net/packet/af_packet.c:4258 [inline]
> 	 packet_set_ring+0xbc0/0x1b50 net/packet/af_packet.c:4342
> 	 packet_setsockopt+0xed7/0x2d90 net/packet/af_packet.c:3695
> 	 __sys_setsockopt+0x29b/0x4d0 net/socket.c:2117
> 	 __do_sys_setsockopt net/socket.c:2133 [inline]
> 	 __se_sys_setsockopt net/socket.c:2130 [inline]
> 	 __x64_sys_setsockopt+0xbe/0x150 net/socket.c:2130
> 	 do_syscall_64+0xfa/0x780 arch/x86/entry/common.c:294
> 	 entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Add kasan_unmap_page_range() which skips empty page table entries instead
> of allocating them.
>
> Fixes: 3c5c3cfb9ef4 ("kasan: support backing vmalloc space with real shadow memory")
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> ---
>  mm/kasan/common.c | 82 +++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 68 insertions(+), 14 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index a1e6273be8c3..e9ba7d8ad324 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -857,22 +857,77 @@ void kasan_unpoison_vmalloc(const void *start, unsigned long size)
>  	kasan_unpoison_shadow(start, size);
>  }
>  
> -static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
> -					void *unused)
> +static void kasan_unmap_pte_range(pmd_t *pmd, unsigned long addr,
> +				unsigned long end)
>  {
> -	unsigned long page;
> +	pte_t *pte;
>  
> -	page = (unsigned long)__va(pte_pfn(*ptep) << PAGE_SHIFT);
> +	pte = pte_offset_kernel(pmd, addr);
> +	do {
> +		pte_t ptent = ptep_get_and_clear(&init_mm, addr, pte);
>  
> -	spin_lock(&init_mm.page_table_lock);
> +		if (!pte_none(ptent))
> +			__free_page(pte_page(ptent));
> +	} while (pte++, addr += PAGE_SIZE, addr != end);
> +}
>  
> -	if (likely(!pte_none(*ptep))) {
> -		pte_clear(&init_mm, addr, ptep);
> -		free_page(page);
> -	}
> -	spin_unlock(&init_mm.page_table_lock);
> +static void kasan_unmap_pmd_range(pud_t *pud, unsigned long addr,
> +				unsigned long end)
> +{
> +	pmd_t *pmd;
> +	unsigned long next;
>  
> -	return 0;
> +	pmd = pmd_offset(pud, addr);
> +	do {
> +		next = pmd_addr_end(addr, end);
> +		if (pmd_none_or_clear_bad(pmd))
> +			continue;
> +		kasan_unmap_pte_range(pmd, addr, next);
> +	} while (pmd++, addr = next, addr != end);
> +}
> +
> +static void kasan_unmap_pud_range(p4d_t *p4d, unsigned long addr,
> +				unsigned long end)
> +{
> +	pud_t *pud;
> +	unsigned long next;
> +
> +	pud = pud_offset(p4d, addr);
> +	do {
> +		next = pud_addr_end(addr, end);
> +		if (pud_none_or_clear_bad(pud))
> +			continue;
> +		kasan_unmap_pmd_range(pud, addr, next);
> +	} while (pud++, addr = next, addr != end);
> +}
> +
> +static void kasan_unmap_p4d_range(pgd_t *pgd, unsigned long addr,
> +				unsigned long end)
> +{
> +	p4d_t *p4d;
> +	unsigned long next;
> +
> +	p4d = p4d_offset(pgd, addr);
> +	do {
> +		next = p4d_addr_end(addr, end);
> +		if (p4d_none_or_clear_bad(p4d))
> +			continue;
> +		kasan_unmap_pud_range(p4d, addr, next);
> +	} while (p4d++, addr = next, addr != end);
> +}
> +
> +static void kasan_unmap_page_range(unsigned long addr, unsigned long end)
> +{
> +	pgd_t *pgd;
> +	unsigned long next;
> +
> +	pgd = pgd_offset_k(addr);
> +	do {
> +		next = pgd_addr_end(addr, end);
> +		if (pgd_none_or_clear_bad(pgd))
> +			continue;
> +		kasan_unmap_p4d_range(pgd, addr, next);
> +	} while (pgd++, addr = next, addr != end);
>  }
>  
>  /*
> @@ -978,9 +1033,8 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
>  	shadow_end = kasan_mem_to_shadow((void *)region_end);
>  
>  	if (shadow_end > shadow_start) {
> -		apply_to_page_range(&init_mm, (unsigned long)shadow_start,
> -				    (unsigned long)(shadow_end - shadow_start),
> -				    kasan_depopulate_vmalloc_pte, NULL);
> +		kasan_unmap_page_range((unsigned long)shadow_start,
> +				    (unsigned long)shadow_end);
>  		flush_tlb_kernel_range((unsigned long)shadow_start,
>  				       (unsigned long)shadow_end);
>  	}
> -- 
> 2.23.0