Messages in this thread Patch in this message | | | Subject | Re: [PATCH] mm, kasan: don't poison boot memory | From | George Kennedy <> | Date | Fri, 19 Feb 2021 18:04:23 -0500 |
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On 2/19/2021 11:45 AM, George Kennedy wrote: > > > On 2/18/2021 7:09 PM, Andrey Konovalov wrote: >> On Fri, Feb 19, 2021 at 1:06 AM George Kennedy >> <george.kennedy@oracle.com> wrote: >>> >>> >>> On 2/18/2021 3:55 AM, David Hildenbrand wrote: >>>> On 17.02.21 21:56, Andrey Konovalov wrote: >>>>> During boot, all non-reserved memblock memory is exposed to the buddy >>>>> allocator. Poisoning all that memory with KASAN lengthens boot time, >>>>> especially on systems with large amount of RAM. This patch makes >>>>> page_alloc to not call kasan_free_pages() on all new memory. >>>>> >>>>> __free_pages_core() is used when exposing fresh memory during system >>>>> boot and when onlining memory during hotplug. This patch adds a new >>>>> FPI_SKIP_KASAN_POISON flag and passes it to __free_pages_ok() through >>>>> free_pages_prepare() from __free_pages_core(). >>>>> >>>>> This has little impact on KASAN memory tracking. >>>>> >>>>> Assuming that there are no references to newly exposed pages >>>>> before they >>>>> are ever allocated, there won't be any intended (but buggy) >>>>> accesses to >>>>> that memory that KASAN would normally detect. >>>>> >>>>> However, with this patch, KASAN stops detecting wild and large >>>>> out-of-bounds accesses that happen to land on a fresh memory page >>>>> that >>>>> was never allocated. This is taken as an acceptable trade-off. >>>>> >>>>> All memory allocated normally when the boot is over keeps getting >>>>> poisoned as usual. >>>>> >>>>> Signed-off-by: Andrey Konovalov <andreyknvl@google.com> >>>>> Change-Id: Iae6b1e4bb8216955ffc14af255a7eaaa6f35324d >>>> Not sure this is the right thing to do, see >>>> >>>> https://lkml.kernel.org/r/bcf8925d-0949-3fe1-baa8-cc536c529860@oracle.com >>>> >>>> >>>> Reversing the order in which memory gets allocated + used during boot >>>> (in a patch by me) might have revealed an invalid memory access during >>>> boot. >>>> >>>> I suspect that that issue would no longer get detected with your >>>> patch, as the invalid memory access would simply not get detected. >>>> Now, I cannot prove that :) >>> Since David's patch we're having trouble with the iBFT ACPI table, >>> which >>> is mapped in via kmap() - see acpi_map() in "drivers/acpi/osl.c". KASAN >>> detects that it is being used after free when ibft_init() accesses the >>> iBFT table, but as of yet we can't find where it get's freed (we've >>> instrumented calls to kunmap()). >> Maybe it doesn't get freed, but what you see is a wild or a large >> out-of-bounds access. Since KASAN marks all memory as freed during the >> memblock->page_alloc transition, such bugs can manifest as >> use-after-frees. > > It gets freed and re-used. By the time the iBFT table is accessed by > ibft_init() the page has been over-written. > > Setting page flags like the following before the call to kmap() > prevents the iBFT table page from being freed:
Cleaned up version:
diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c index 0418feb..8f0a8e7 100644 --- a/drivers/acpi/osl.c +++ b/drivers/acpi/osl.c @@ -287,9 +287,12 @@ static void __iomem *acpi_map(acpi_physical_address pg_off, unsigned long pg_sz)
pfn = pg_off >> PAGE_SHIFT; if (should_use_kmap(pfn)) { + struct page *page = pfn_to_page(pfn); + if (pg_sz > PAGE_SIZE) return NULL; - return (void __iomem __force *)kmap(pfn_to_page(pfn)); + SetPageReserved(page); + return (void __iomem __force *)kmap(page); } else return acpi_os_ioremap(pg_off, pg_sz); } @@ -299,9 +302,12 @@ static void acpi_unmap(acpi_physical_address pg_off, void __iomem *vaddr) unsigned long pfn;
pfn = pg_off >> PAGE_SHIFT; - if (should_use_kmap(pfn)) - kunmap(pfn_to_page(pfn)); - else + if (should_use_kmap(pfn)) { + struct page *page = pfn_to_page(pfn); + + ClearPageReserved(page); + kunmap(page); + } else iounmap(vaddr); }
David, the above works, but wondering why it is now necessary. kunmap() is not hit. What other ways could a page mapped via kmap() be unmapped? Thank you, George
> > diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c > index 0418feb..41c1bbd 100644 > --- a/drivers/acpi/osl.c > +++ b/drivers/acpi/osl.c > @@ -287,9 +287,14 @@ static void __iomem > *acpi_map(acpi_physical_address pg_off, unsigned long pg_sz) > > pfn = pg_off >> PAGE_SHIFT; > if (should_use_kmap(pfn)) { > + struct page *page = pfn_to_page(pfn); > + > if (pg_sz > PAGE_SIZE) > return NULL; > - return (void __iomem __force *)kmap(pfn_to_page(pfn)); > + > + page->flags |= ((1UL << PG_unevictable) | (1UL << > PG_reserved) | (1UL << PG_locked)); > + > + return (void __iomem __force *)kmap(page); > } else > return acpi_os_ioremap(pg_off, pg_sz); > } > > Just not sure of the correct way to set the page flags. > > George >
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