Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1546266 > unrolled thread

[PATCH v2 1/2] x86/efi: don't allocate memmap through memblock after mm_init()

Back to article view | Back to linux.kernel

Contents

  [PATCH v2 1/2] x86/efi: don't allocate memmap through memblock after mm_init() Nicolai Stange <nicstange@gmail.com> - 2016-12-22 11:30 +0100
    Re: [PATCH v2 1/2] x86/efi: don't allocate memmap through memblock  after mm_init() Matt Fleming <matt@codeblueprint.co.uk> - 2016-12-23 16:00 +0100
      Re: [PATCH v2 1/2] x86/efi: don't allocate memmap through memblock after mm_init() Nicolai Stange <nicstange@gmail.com> - 2016-12-23 22:20 +0100

#1546266 — [PATCH v2 1/2] x86/efi: don't allocate memmap through memblock after mm_init()

With commit 4bc9f92e64c8 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid
copying image data"), efi_bgrt_init() calls into the memblock allocator
through efi_mem_reserve() => efi_arch_mem_reserve() *after* mm_init()
has been called.

Indeed, KASAN reports a bad read access later on in
efi_free_boot_services():

  BUG: KASAN: use-after-free in efi_free_boot_services+0xae/0x24c
            at addr ffff88022de12740
  Read of size 4 by task swapper/0/0
  page:ffffea0008b78480 count:0 mapcount:-127
  mapping:          (null) index:0x1 flags: 0x5fff8000000000()
  [...]
  Call Trace:
   dump_stack+0x68/0x9f
   kasan_report_error+0x4c8/0x500
   kasan_report+0x58/0x60
   __asan_load4+0x61/0x80
   efi_free_boot_services+0xae/0x24c
   start_kernel+0x527/0x562
   x86_64_start_reservations+0x24/0x26
   x86_64_start_kernel+0x157/0x17a
   start_cpu+0x5/0x14

The instruction at the given address is the first read from the memmap's
memory, i.e. the read of md->type in efi_free_boot_services().

Note that the writes earlier in efi_arch_mem_reserve() don't splat because
they're done through early_memremap()ed addresses.

So, after memblock is gone, allocations should be done through the "normal"
page allocator. Introduce a helper, efi_memmap_alloc() for this. Use
it from efi_arch_mem_reserve() and from efi_free_boot_services() as well.

Fixes: 4bc9f92e64c8 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid copying image data")
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
---
 arch/x86/platform/efi/quirks.c |  4 ++--
 drivers/firmware/efi/memmap.c  | 38 ++++++++++++++++++++++++++++++++++++++
 include/linux/efi.h            |  1 +
 3 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index 10aca63a50d7..30031d5293c4 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -214,7 +214,7 @@ void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size)
 
 	new_size = efi.memmap.desc_size * num_entries;
 
-	new_phys = memblock_alloc(new_size, 0);
+	new_phys = efi_memmap_alloc(num_entries);
 	if (!new_phys) {
 		pr_err("Could not allocate boot services memmap\n");
 		return;
@@ -355,7 +355,7 @@ void __init efi_free_boot_services(void)
 	}
 
 	new_size = efi.memmap.desc_size * num_entries;
-	new_phys = memblock_alloc(new_size, 0);
+	new_phys = efi_memmap_alloc(num_entries);
 	if (!new_phys) {
 		pr_err("Failed to allocate new EFI memmap\n");
 		return;
diff --git a/drivers/firmware/efi/memmap.c b/drivers/firmware/efi/memmap.c
index f03ddecd232b..78686443cb37 100644
--- a/drivers/firmware/efi/memmap.c
+++ b/drivers/firmware/efi/memmap.c
@@ -9,6 +9,44 @@
 #include <linux/efi.h>
 #include <linux/io.h>
 #include <asm/early_ioremap.h>
+#include <linux/memblock.h>
+#include <linux/slab.h>
+
+static phys_addr_t __init __efi_memmap_alloc_early(unsigned long size)
+{
+	return memblock_alloc(size, 0);
+}
+
+static phys_addr_t __init __efi_memmap_alloc_late(unsigned long size)
+{
+	unsigned int order = get_order(size);
+	struct page *p = alloc_pages(GFP_KERNEL, order);
+
+	if (!p)
+		return 0;
+
+	return PFN_PHYS(page_to_pfn(p));
+}
+
+/**
+ * efi_memmap_alloc - Allocate memory for the EFI memory map
+ * @num_entries: Number of entries in the allocated map.
+ *
+ * Depending on whether mm_init() has already been invoked or not,
+ * either memblock or "normal" page allocation is used.
+ *
+ * Returns the physical address of the allocated memory map on
+ * success, zero on failure.
+ */
+phys_addr_t __init efi_memmap_alloc(unsigned int num_entries)
+{
+	unsigned long size = num_entries * efi.memmap.desc_size;
+
+	if (slab_is_available())
+		return __efi_memmap_alloc_late(size);
+
+	return __efi_memmap_alloc_early(size);
+}
 
 /**
  * __efi_memmap_init - Common code for mapping the EFI memory map
diff --git a/include/linux/efi.h b/include/linux/efi.h
index a07a476178cd..0c5420208c40 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -950,6 +950,7 @@ static inline efi_status_t efi_query_variable_store(u32 attributes,
 #endif
 extern void __iomem *efi_lookup_mapped_addr(u64 phys_addr);
 
+extern phys_addr_t __init efi_memmap_alloc(unsigned int num_entries);
 extern int __init efi_memmap_init_early(struct efi_memory_map_data *data);
 extern int __init efi_memmap_init_late(phys_addr_t addr, unsigned long size);
 extern void __init efi_memmap_unmap(void);
-- 
2.11.0

[toc] | [next] | [standalone]

#1546885 — Re: [PATCH v2 1/2] x86/efi: don't allocate memmap through memblock after mm_init()

On Thu, 22 Dec, at 11:23:39AM, Nicolai Stange wrote:
> With commit 4bc9f92e64c8 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid
> copying image data"), efi_bgrt_init() calls into the memblock allocator
> through efi_mem_reserve() => efi_arch_mem_reserve() *after* mm_init()
> has been called.
> 
> Indeed, KASAN reports a bad read access later on in
> efi_free_boot_services():
> 
>   BUG: KASAN: use-after-free in efi_free_boot_services+0xae/0x24c
>             at addr ffff88022de12740
>   Read of size 4 by task swapper/0/0
>   page:ffffea0008b78480 count:0 mapcount:-127
>   mapping:          (null) index:0x1 flags: 0x5fff8000000000()
>   [...]
>   Call Trace:
>    dump_stack+0x68/0x9f
>    kasan_report_error+0x4c8/0x500
>    kasan_report+0x58/0x60
>    __asan_load4+0x61/0x80
>    efi_free_boot_services+0xae/0x24c
>    start_kernel+0x527/0x562
>    x86_64_start_reservations+0x24/0x26
>    x86_64_start_kernel+0x157/0x17a
>    start_cpu+0x5/0x14
> 
> The instruction at the given address is the first read from the memmap's
> memory, i.e. the read of md->type in efi_free_boot_services().
> 
> Note that the writes earlier in efi_arch_mem_reserve() don't splat because
> they're done through early_memremap()ed addresses.
> 
> So, after memblock is gone, allocations should be done through the "normal"
> page allocator. Introduce a helper, efi_memmap_alloc() for this. Use
> it from efi_arch_mem_reserve() and from efi_free_boot_services() as well.
> 
> Fixes: 4bc9f92e64c8 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid copying image data")
> Signed-off-by: Nicolai Stange <nicstange@gmail.com>
> ---
>  arch/x86/platform/efi/quirks.c |  4 ++--
>  drivers/firmware/efi/memmap.c  | 38 ++++++++++++++++++++++++++++++++++++++
>  include/linux/efi.h            |  1 +
>  3 files changed, 41 insertions(+), 2 deletions(-)

Nice catch. Could you also modify efi_fake_memmap() to use your new
efi_memmap_alloc() function for consistency (note that all
memblock_alloc()s should probably be PAGE_SIZE aligned like the
fakemem code)?

[toc] | [prev] | [next] | [standalone]

#1546973

Matt Fleming <matt@codeblueprint.co.uk> writes:

> On Thu, 22 Dec, at 11:23:39AM, Nicolai Stange wrote:
>> So, after memblock is gone, allocations should be done through the "normal"
>> page allocator. Introduce a helper, efi_memmap_alloc() for this. Use
>> it from efi_arch_mem_reserve() and from efi_free_boot_services() as well.
>> 
>> Fixes: 4bc9f92e64c8 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid copying image data")
>> Signed-off-by: Nicolai Stange <nicstange@gmail.com>

> Could you also modify efi_fake_memmap() to use your new
> efi_memmap_alloc() function for consistency

Sure.

I'm planning to submit another set of patches addressing the (bounded)
memmap leaking in anything calling efi_memmap_unmap() though. In the
course of doing so, the memmap allocation sites will get touched anyway:
I'll have to store some information about how the memmap's memory has
been obtained.

> (note that all memblock_alloc()s should probably be PAGE_SIZE aligned
> like the fakemem code)?

Ok, but I'd really like to understand why: I can't find anything in
neither the code nor in the UEFI spec requiring this. And up to now,
efi_arch_mem_reserve() as well as efi_free_boot_services() used to do
those unaligned allocations...

In light of this, is there really a necessity for using whole page
allocations after mm_init() or would kmalloc() suffice here?
Provided that the memremap bits get adjusted accordingly, of course.

So, I'm thinking of turning the ->late boolean into a tristate like the
following:

Memory allocated by | Memory mapped through
--------------------|----------------------
memblock            | early_memremap
memblock            | memremap
kmalloc             | -

Neglecting slub overhead, the use of kmalloc() over alloc_pages() would
save 4096 - 12*40 == 3616 Bytes on my system with its 12 entries under
/sys/firmware/efi/runtime-map/. Not really critical, but if it comes for
free, why not?


Thanks,

Nicolai

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web