[PATCH v2 0/1] mm: kfence: fix unexpected leak scan on kfence pool

[PATCH v2 0/1] mm: kfence: fix unexpected leak scan on kfence pool

[yee.lee]

From: Yee Lee <yee.lee@mediatek.com>

Since the latest patches of kmemleak separated its address management 
to two rb-trees, phys and virt, the kmemleak_free failed to free kfence_pool
from the virt tree. It caused unexpected scan the blocks and triggered
kfence faults.

Reference: 
https://lore.kernel.org/linux-mm/20220611035551.1823303-1-patrick.wang.shcn@gmail.com/

 ==================================================================
 BUG: KFENCE: invalid read in scan_block+0x13c/0x838

  Invalid read at 0x000000003dc26873:
  scan_block+0x13c/0x838
  scan_gray_list+0x1f0/0x478
  kmemleak_scan+0x63c/0xd64
  kmemleak_write+0x618/0x8cc
  full_proxy_write+0x70/0x138
  vfs_write+0x108/0x314
  ksys_write+0x7c/0x14c
  __arm64_sys_write+0x20/0x30
  el0_svc_common+0xa8/0x144
  do_el0_svc+0x30/0xd4
  el0_svc+0x38/0x15c
  el0t_64_sync_handler+0x88/0xf8
  el0t_64_sync+0x1a0/0x1a4

 CPU: 0 PID: 128 Comm: sh Not tainted 5.18.0-mainline-40996-g7d83a175ff4a-dirty #1
 Hardware name: linux,dummy-virt (DT)
 ==================================================================

This patch applies kmemleak_ignore_phys() to replace the original kmemleak_free and
adapts it to the late enabling case. 

v1->v2:
 - use kmemleak_ignore_phys() to bypass the scanning.
 - move out the freeing opeartion from late enabling as it's trivial.

Yee Lee (1):
  mm: kfence: apply kmemleak_ignore_phys on early allocated pool

 mm/kfence/core.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

-- 
2.18.0


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[PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[yee.lee]

From: Yee Lee <yee.lee@mediatek.com>

This patch solves two issues.

(1) The pool allocated by memblock needs to unregister from
kmemleak scanning. Apply kmemleak_ignore_phys to replace the
original kmemleak_free as its address now is stored in the phys tree.

(2) The pool late allocated by page-alloc doesn't need to unregister.
Move out the freeing operation from its call path.

Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Yee Lee <yee.lee@mediatek.com>
---
 mm/kfence/core.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 4e7cd4c8e687..32a4a75e820c 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -600,14 +600,6 @@ static unsigned long kfence_init_pool(void)
 		addr += 2 * PAGE_SIZE;
 	}
 
-	/*
-	 * The pool is live and will never be deallocated from this point on.
-	 * Remove the pool object from the kmemleak object tree, as it would
-	 * otherwise overlap with allocations returned by kfence_alloc(), which
-	 * are registered with kmemleak through the slab post-alloc hook.
-	 */
-	kmemleak_free(__kfence_pool);
-
 	return 0;
 }
 
@@ -620,8 +612,16 @@ static bool __init kfence_init_pool_early(void)
 
 	addr = kfence_init_pool();
 
-	if (!addr)
+	if (!addr) {
+		/*
+		 * The pool is live and will never be deallocated from this point on.
+		 * Ignore the pool object from the kmemleak phys object tree, as it would
+		 * otherwise overlap with allocations returned by kfence_alloc(), which
+		 * are registered with kmemleak through the slab post-alloc hook.
+		 */
+		kmemleak_ignore_phys(__pa(__kfence_pool));
 		return true;
+	}
 
 	/*
 	 * Only release unprotected pages, and do not try to go back and change
-- 
2.18.0


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Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[Marco Elver]

On Tue, 28 Jun 2022 at 13:37, yee.lee via kasan-dev
<kasan-dev@googlegroups.com> wrote:
>
> From: Yee Lee <yee.lee@mediatek.com>
>
> This patch solves two issues.
>
> (1) The pool allocated by memblock needs to unregister from
> kmemleak scanning. Apply kmemleak_ignore_phys to replace the
> original kmemleak_free as its address now is stored in the phys tree.
>
> (2) The pool late allocated by page-alloc doesn't need to unregister.
> Move out the freeing operation from its call path.
>
> Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
> Suggested-by: Marco Elver <elver@google.com>
> Signed-off-by: Yee Lee <yee.lee@mediatek.com>

Reviewed-by: Marco Elver <elver@google.com>

Does this want a Fixes tag?

> ---
>  mm/kfence/core.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 4e7cd4c8e687..32a4a75e820c 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -600,14 +600,6 @@ static unsigned long kfence_init_pool(void)
>                 addr += 2 * PAGE_SIZE;
>         }
>
> -       /*
> -        * The pool is live and will never be deallocated from this point on.
> -        * Remove the pool object from the kmemleak object tree, as it would
> -        * otherwise overlap with allocations returned by kfence_alloc(), which
> -        * are registered with kmemleak through the slab post-alloc hook.
> -        */
> -       kmemleak_free(__kfence_pool);
> -
>         return 0;
>  }
>
> @@ -620,8 +612,16 @@ static bool __init kfence_init_pool_early(void)
>
>         addr = kfence_init_pool();
>
> -       if (!addr)
> +       if (!addr) {
> +               /*
> +                * The pool is live and will never be deallocated from this point on.
> +                * Ignore the pool object from the kmemleak phys object tree, as it would
> +                * otherwise overlap with allocations returned by kfence_alloc(), which
> +                * are registered with kmemleak through the slab post-alloc hook.
> +                */
> +               kmemleak_ignore_phys(__pa(__kfence_pool));
>                 return true;
> +       }
>
>         /*
>          * Only release unprotected pages, and do not try to go back and change
> --
> 2.18.0

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Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[Catalin Marinas]

On Tue, Jun 28, 2022 at 07:37:11PM +0800, yee.lee@mediatek.com wrote:
> From: Yee Lee <yee.lee@mediatek.com>
> 
> This patch solves two issues.
> 
> (1) The pool allocated by memblock needs to unregister from
> kmemleak scanning. Apply kmemleak_ignore_phys to replace the
> original kmemleak_free as its address now is stored in the phys tree.
> 
> (2) The pool late allocated by page-alloc doesn't need to unregister.
> Move out the freeing operation from its call path.
> 
> Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
> Suggested-by: Marco Elver <elver@google.com>
> Signed-off-by: Yee Lee <yee.lee@mediatek.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

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Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[Geert Uytterhoeven]

Hi Yee,

On Tue, Jun 28, 2022 at 1:42 PM <yee.lee@mediatek.com> wrote:
> From: Yee Lee <yee.lee@mediatek.com>
>
> This patch solves two issues.
>
> (1) The pool allocated by memblock needs to unregister from
> kmemleak scanning. Apply kmemleak_ignore_phys to replace the
> original kmemleak_free as its address now is stored in the phys tree.
>
> (2) The pool late allocated by page-alloc doesn't need to unregister.
> Move out the freeing operation from its call path.
>
> Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
> Suggested-by: Marco Elver <elver@google.com>
> Signed-off-by: Yee Lee <yee.lee@mediatek.com>

Thank you, this fixes the storm of

    BUG: KFENCE: invalid read in scan_block+0x78/0x130
    BUG: KFENCE: use-after-free read in scan_block+0x78/0x130
    BUG: KFENCE: out-of-bounds read in scan_block+0x78/0x130

messages I was seeing on arm64.

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[Andrew Morton]

On Fri, 15 Jul 2022 10:17:43 +0200 Geert Uytterhoeven <geert@linux-m68k.org> wrote:

> On Tue, Jun 28, 2022 at 1:42 PM <yee.lee@mediatek.com> wrote:
> > From: Yee Lee <yee.lee@mediatek.com>
> >
> > This patch solves two issues.
> >
> > (1) The pool allocated by memblock needs to unregister from
> > kmemleak scanning. Apply kmemleak_ignore_phys to replace the
> > original kmemleak_free as its address now is stored in the phys tree.
> >
> > (2) The pool late allocated by page-alloc doesn't need to unregister.
> > Move out the freeing operation from its call path.
> >
> > Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
> > Suggested-by: Marco Elver <elver@google.com>
> > Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> 
> Thank you, this fixes the storm of
> 
>     BUG: KFENCE: invalid read in scan_block+0x78/0x130
>     BUG: KFENCE: use-after-free read in scan_block+0x78/0x130
>     BUG: KFENCE: out-of-bounds read in scan_block+0x78/0x130
> 
> messages I was seeing on arm64.

Thanks, but...

- It would be great if we could identify a Fixes: for this.

- This patch has been accused of crashing the kernel:

	https://lkml.kernel.org/r/YsFeUHkrFTQ7T51Q@xsang-OptiPlex-9020

  Do we think that report is bogus?

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Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[Geert Uytterhoeven]

Hi Andrew,

On Sat, Jul 16, 2022 at 1:33 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> On Fri, 15 Jul 2022 10:17:43 +0200 Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Tue, Jun 28, 2022 at 1:42 PM <yee.lee@mediatek.com> wrote:
> > > From: Yee Lee <yee.lee@mediatek.com>
> > >
> > > This patch solves two issues.
> > >
> > > (1) The pool allocated by memblock needs to unregister from
> > > kmemleak scanning. Apply kmemleak_ignore_phys to replace the
> > > original kmemleak_free as its address now is stored in the phys tree.
> > >
> > > (2) The pool late allocated by page-alloc doesn't need to unregister.
> > > Move out the freeing operation from its call path.
> > >
> > > Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
> > > Suggested-by: Marco Elver <elver@google.com>
> > > Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> >
> > Thank you, this fixes the storm of
> >
> >     BUG: KFENCE: invalid read in scan_block+0x78/0x130
> >     BUG: KFENCE: use-after-free read in scan_block+0x78/0x130
> >     BUG: KFENCE: out-of-bounds read in scan_block+0x78/0x130
> >
> > messages I was seeing on arm64.
>
> Thanks, but...
>
> - It would be great if we could identify a Fixes: for this.

IIRC, I started seeing the issue with "[PATCH v4 3/4] mm:
kmemleak: add rbtree and store physical address for objects
allocated with PA" (i.e. commit 0c24e061196c21d5 ("mm: kmemleak:
add rbtree and store physical address for objects allocated
with PA")) of series "[PATCH v4 0/4] mm: kmemleak: store objects
allocated with physical address separately and check when scan"
(https://lore.kernel.org/all/20220611035551.1823303-1-patrick.wang.shcn@gmail.com),
in an arm64 config that had enabled kfence.
So I think this patch is sort of a dependency for that series.

I had cherry-picked that series after bisecting a regression to
commit 23c2d497de21f258 ("mm: kmemleak: take a full lowmem check in
kmemleak_*_phys()") in v5.18-rc3, and having a look around.

> - This patch has been accused of crashing the kernel:
>
>         https://lkml.kernel.org/r/YsFeUHkrFTQ7T51Q@xsang-OptiPlex-9020
>
>   Do we think that report is bogus?

I think all of this is highly architecture-specific...

Gr{oetje,eeting}s,

                        Geert

--
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In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[Marco Elver]

On Sat, 16 Jul 2022 at 20:43, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
[...]
> > - This patch has been accused of crashing the kernel:
> >
> >         https://lkml.kernel.org/r/YsFeUHkrFTQ7T51Q@xsang-OptiPlex-9020
> >
> >   Do we think that report is bogus?
>
> I think all of this is highly architecture-specific...

The report can be reproduced on i386 with CONFIG_X86_PAE=y. But e.g.
mm/memblock.c:memblock_free() is also guilty of using __pa() on
previously memblock_alloc()'d addresses. Looking at the phys addr
before memblock_alloc() does virt_to_phys(), the result of __pa()
looks correct even on PAE, at least for the purpose of passing it on
to kmemleak(). So I don't know what that BUG_ON(slow_virt_to_phys() !=
phys_addr) is supposed to tell us here.

Ideas?

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Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[Catalin Marinas]

On Sat, Jul 16, 2022 at 08:43:06PM +0200, Geert Uytterhoeven wrote:
> On Sat, Jul 16, 2022 at 1:33 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> > On Fri, 15 Jul 2022 10:17:43 +0200 Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > On Tue, Jun 28, 2022 at 1:42 PM <yee.lee@mediatek.com> wrote:
> > > > From: Yee Lee <yee.lee@mediatek.com>
> > > >
> > > > This patch solves two issues.
> > > >
> > > > (1) The pool allocated by memblock needs to unregister from
> > > > kmemleak scanning. Apply kmemleak_ignore_phys to replace the
> > > > original kmemleak_free as its address now is stored in the phys tree.
> > > >
> > > > (2) The pool late allocated by page-alloc doesn't need to unregister.
> > > > Move out the freeing operation from its call path.
> > > >
> > > > Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
> > > > Suggested-by: Marco Elver <elver@google.com>
> > > > Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> > >
> > > Thank you, this fixes the storm of
> > >
> > >     BUG: KFENCE: invalid read in scan_block+0x78/0x130
> > >     BUG: KFENCE: use-after-free read in scan_block+0x78/0x130
> > >     BUG: KFENCE: out-of-bounds read in scan_block+0x78/0x130
> > >
> > > messages I was seeing on arm64.
> >
> > Thanks, but...
> >
> > - It would be great if we could identify a Fixes: for this.
> 
> IIRC, I started seeing the issue with "[PATCH v4 3/4] mm:
> kmemleak: add rbtree and store physical address for objects
> allocated with PA" (i.e. commit 0c24e061196c21d5 ("mm: kmemleak:
> add rbtree and store physical address for objects allocated
> with PA")) of series "[PATCH v4 0/4] mm: kmemleak: store objects
> allocated with physical address separately and check when scan"
> (https://lore.kernel.org/all/20220611035551.1823303-1-patrick.wang.shcn@gmail.com),
> in an arm64 config that had enabled kfence.

Yes, I think it fixes 0c24e061196c21d5 since after that commit, the
kmemleak_free() no longer worked as expected on physically allocated
objects.

-- 
Catalin

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Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[Andrew Morton]

On Mon, 18 Jul 2022 16:26:25 +0200 Marco Elver <elver@google.com> wrote:

> On Sat, 16 Jul 2022 at 20:43, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> [...]
> > > - This patch has been accused of crashing the kernel:
> > >
> > >         https://lkml.kernel.org/r/YsFeUHkrFTQ7T51Q@xsang-OptiPlex-9020
> > >
> > >   Do we think that report is bogus?
> >
> > I think all of this is highly architecture-specific...
> 
> The report can be reproduced on i386 with CONFIG_X86_PAE=y. But e.g.
> mm/memblock.c:memblock_free() is also guilty of using __pa() on
> previously memblock_alloc()'d addresses. Looking at the phys addr
> before memblock_alloc() does virt_to_phys(), the result of __pa()
> looks correct even on PAE, at least for the purpose of passing it on
> to kmemleak(). So I don't know what that BUG_ON(slow_virt_to_phys() !=
> phys_addr) is supposed to tell us here.
> 

It's only been nine years, so I'm sure Dave can remember why he added
it ;)

		BUG_ON(slow_virt_to_phys((void *)x) != phys_addr);

in arch/x86/mm/physaddr.c:__phys_addr().


This kfence patch does seem to be desirable, but we can't proceed if
it's resulting in kernel crashes.


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Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[Dave Hansen]

On 7/19/22 16:13, Andrew Morton wrote:
> On Mon, 18 Jul 2022 16:26:25 +0200 Marco Elver <elver@google.com> wrote:
> 
>> On Sat, 16 Jul 2022 at 20:43, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>> [...]
>>>> - This patch has been accused of crashing the kernel:
>>>>
>>>>         https://lkml.kernel.org/r/YsFeUHkrFTQ7T51Q@xsang-OptiPlex-9020
>>>>
>>>>   Do we think that report is bogus?
>>> I think all of this is highly architecture-specific...
>> The report can be reproduced on i386 with CONFIG_X86_PAE=y. But e.g.
>> mm/memblock.c:memblock_free() is also guilty of using __pa() on
>> previously memblock_alloc()'d addresses. Looking at the phys addr
>> before memblock_alloc() does virt_to_phys(), the result of __pa()
>> looks correct even on PAE, at least for the purpose of passing it on
>> to kmemleak(). So I don't know what that BUG_ON(slow_virt_to_phys() !=
>> phys_addr) is supposed to tell us here.
>>
> It's only been nine years, so I'm sure Dave can remember why he added
> it ;)
> 
> 		BUG_ON(slow_virt_to_phys((void *)x) != phys_addr);
> 
> in arch/x86/mm/physaddr.c:__phys_addr().

I think I intended it to double check that the linear map is *actually*
a linear map for 'x'.  Sure, we can use the "x - PAGE_OFFSET" shortcut,
but did it turn out to be actually accurate for the address it was handed?

I'd be curious what the page tables actually say for the address that's
causing problems.

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Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early allocated pool

[Marco Elver]

[+x86 maintainers ...]

On Wed, 20 Jul 2022 at 01:22, Dave Hansen <dave.hansen@intel.com> wrote:
> On 7/19/22 16:13, Andrew Morton wrote:
> > On Mon, 18 Jul 2022 16:26:25 +0200 Marco Elver <elver@google.com> wrote:
> >
> >> On Sat, 16 Jul 2022 at 20:43, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> >> [...]
> >>>> - This patch has been accused of crashing the kernel:
> >>>>
> >>>>         https://lkml.kernel.org/r/YsFeUHkrFTQ7T51Q@xsang-OptiPlex-9020
> >>>>
> >>>>   Do we think that report is bogus?
> >>> I think all of this is highly architecture-specific...
> >> The report can be reproduced on i386 with CONFIG_X86_PAE=y. But e.g.
> >> mm/memblock.c:memblock_free() is also guilty of using __pa() on
> >> previously memblock_alloc()'d addresses. Looking at the phys addr
> >> before memblock_alloc() does virt_to_phys(), the result of __pa()
> >> looks correct even on PAE, at least for the purpose of passing it on
> >> to kmemleak(). So I don't know what that BUG_ON(slow_virt_to_phys() !=
> >> phys_addr) is supposed to tell us here.
> >>
> > It's only been nine years, so I'm sure Dave can remember why he added
> > it ;)
> >
> >               BUG_ON(slow_virt_to_phys((void *)x) != phys_addr);
> >
> > in arch/x86/mm/physaddr.c:__phys_addr().
>
> I think I intended it to double check that the linear map is *actually*
> a linear map for 'x'.  Sure, we can use the "x - PAGE_OFFSET" shortcut,
> but did it turn out to be actually accurate for the address it was handed?
>
> I'd be curious what the page tables actually say for the address that's
> causing problems.

test robot just reminded us again:
https://lore.kernel.org/all/YufXncrWhJZH0ifB@xsang-OptiPlex-9020/T/#u

Few things I noticed:

* mm/memblock.c's memblock_free() also uses __pa() to convert back to
physical address. Presumably that's also wrong. What should be used
instead?

* kmemleak happily converts phys_addr_t to unsigned long everywhere,
but with i386 PAE, this will narrow a 64-bit address to a 32-bit
address. Is that correct? Does kmemleak need a "depends on 64BIT ||
!PHYS_ADDR_T_64BIT"?

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