Re: [PATCH 4/5 v16] ARM: Initialize the mapping of KASan shadow memory

From: Ard Biesheuvel <ardb@kernel.org>
To: Mike Rapoport <rppt@linux.ibm.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>,
	Ahmad Fatoum <a.fatoum@pengutronix.de>,
	Arnd Bergmann <arnd@arndb.de>,
	Abbott Liu <liuwenliang@huawei.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Russell King <linux@armlinux.org.uk>,
	kasan-dev <kasan-dev@googlegroups.com>,
	Alexander Potapenko <glider@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 4/5 v16] ARM: Initialize the mapping of KASan shadow memory
Date: Mon, 19 Oct 2020 11:42:44 +0200	[thread overview]
Message-ID: <CAMj1kXGgrtj79UQ7Ei5NEEQ1_ALTJRVALFnjOmhZLb_4tSHauQ@mail.gmail.com> (raw)
In-Reply-To: <20201019093421.GA455883@linux.ibm.com>

On Mon, 19 Oct 2020 at 11:37, Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Mon, Oct 19, 2020 at 10:41:39AM +0200, Linus Walleij wrote:
> > This patch initializes KASan shadow region's page table and memory.
> > There are two stage for KASan initializing:
> >
> > 1. At early boot stage the whole shadow region is mapped to just
> >    one physical page (kasan_zero_page). It is finished by the function
> >    kasan_early_init which is called by __mmap_switched(arch/arm/kernel/
> >    head-common.S)
> >
> > 2. After the calling of paging_init, we use kasan_zero_page as zero
> >    shadow for some memory that KASan does not need to track, and we
> >    allocate a new shadow space for the other memory that KASan need to
> >    track. These issues are finished by the function kasan_init which is
> >    call by setup_arch.
> >
> > When using KASan we also need to increase the THREAD_SIZE_ORDER
> > from 1 to 2 as the extra calls for shadow memory uses quite a bit
> > of stack.
> >
> > As we need to make a temporary copy of the PGD when setting up
> > shadow memory we create a helpful PGD_SIZE definition for both
> > LPAE and non-LPAE setups.
> >
> > The KASan core code unconditionally calls pud_populate() so this
> > needs to be changed from BUG() to do {} while (0) when building
> > with KASan enabled.
> >
> > After the initial development by Andre Ryabinin several modifications
> > have been made to this code:
> >
> > Abbott Liu <liuwenliang@huawei.com>
> > - Add support ARM LPAE: If LPAE is enabled, KASan shadow region's
> >   mapping table need be copied in the pgd_alloc() function.
> > - Change kasan_pte_populate,kasan_pmd_populate,kasan_pud_populate,
> >   kasan_pgd_populate from .meminit.text section to .init.text section.
> >   Reported by Florian Fainelli <f.fainelli@gmail.com>
> >
> > Linus Walleij <linus.walleij@linaro.org>:
> > - Drop the custom mainpulation of TTBR0 and just use
> >   cpu_switch_mm() to switch the pgd table.
> > - Adopt to handle 4th level page tabel folding.
> > - Rewrite the entire page directory and page entry initialization
> >   sequence to be recursive based on ARM64:s kasan_init.c.
> >
> > Ard Biesheuvel <ardb@kernel.org>:
> > - Necessary underlying fixes.
> > - Crucial bug fixes to the memory set-up code.
> >
> > Cc: Alexander Potapenko <glider@google.com>
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Cc: kasan-dev@googlegroups.com
> > Cc: Mike Rapoport <rppt@linux.ibm.com>
> > Co-developed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> > Co-developed-by: Abbott Liu <liuwenliang@huawei.com>
> > Co-developed-by: Ard Biesheuvel <ardb@kernel.org>
> > Acked-by: Mike Rapoport <rppt@linux.ibm.com>
> > Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
> > Tested-by: Ard Biesheuvel <ardb@kernel.org> # QEMU/KVM/mach-virt/LPAE/8G
> > Tested-by: Florian Fainelli <f.fainelli@gmail.com> # Brahma SoCs
> > Tested-by: Ahmad Fatoum <a.fatoum@pengutronix.de> # i.MX6Q
> > Reported-by: Russell King - ARM Linux <linux@armlinux.org.uk>
> > Reported-by: Florian Fainelli <f.fainelli@gmail.com>
> > Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> > Signed-off-by: Abbott Liu <liuwenliang@huawei.com>
> > Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> > ---
>
> ...
>
> > +     cpu_switch_mm(tmp_pgd_table, &init_mm);
> > +     local_flush_tlb_all();
> > +
> > +     clear_pgds(KASAN_SHADOW_START, KASAN_SHADOW_END);
> > +
> > +     kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
> > +                                 kasan_mem_to_shadow((void *)-1UL) + 1);
> > +
> > +     for_each_memblock(memory, reg) {
> > +             void *start = __va(reg->base);
> > +             void *end = __va(reg->base + reg->size);
> > +
>
> I've killed for_each_memblock() recently and we have now
>
>         for_each_mem_range(idx, &pa_start, &pa_end)
>
> instead.
>

Will the enumeration include NOMAP regions as well? We could actually
omit them here, since they don't need KASAN shadow.

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