[tip: x86/urgent] x86/mm: Avoid using set_pgd() outside of real PGD pages

[tip: x86/urgent] x86/mm: Avoid using set_pgd() outside of real PGD pages

[tip-bot2 for Lee Jones]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     d082d48737c75d2b3cc1f972b8c8674c25131534
Gitweb:        https://git.kernel.org/tip/d082d48737c75d2b3cc1f972b8c8674c25131534
Author:        Lee Jones <lee@kernel.org>
AuthorDate:    Wed, 14 Jun 2023 17:38:54 +01:00
Committer:     Dave Hansen <dave.hansen@linux.intel.com>
CommitterDate: Fri, 16 Jun 2023 11:46:42 -07:00

x86/mm: Avoid using set_pgd() outside of real PGD pages

KPTI keeps around two PGDs: one for userspace and another for the
kernel. Among other things, set_pgd() contains infrastructure to
ensure that updates to the kernel PGD are reflected in the user PGD
as well.

One side-effect of this is that set_pgd() expects to be passed whole
pages.  Unfortunately, init_trampoline_kaslr() passes in a single entry:
'trampoline_pgd_entry'.

When KPTI is on, set_pgd() will update 'trampoline_pgd_entry' (an
8-Byte globally stored [.bss] variable) and will then proceed to
replicate that value into the non-existent neighboring user page
(located +4k away), leading to the corruption of other global [.bss]
stored variables.

Fix it by directly assigning 'trampoline_pgd_entry' and avoiding
set_pgd().

[ dhansen: tweak subject and changelog ]

Fixes: 0925dda5962e ("x86/mm/KASLR: Use only one PUD entry for real mode trampoline")
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/all/20230614163859.924309-1-lee@kernel.org/g
---
 arch/x86/mm/kaslr.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 557f0fe..37db264 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -172,10 +172,10 @@ void __meminit init_trampoline_kaslr(void)
 		set_p4d(p4d_tramp,
 			__p4d(_KERNPG_TABLE | __pa(pud_page_tramp)));
 
-		set_pgd(&trampoline_pgd_entry,
-			__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp)));
+		trampoline_pgd_entry =
+			__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp));
 	} else {
-		set_pgd(&trampoline_pgd_entry,
-			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));
+		trampoline_pgd_entry =
+			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp));
 	}
 }

Re: [tip: x86/urgent] x86/mm: Avoid using set_pgd() outside of real PGD pages

[Lee Jones]

Dear Stable,

On Fri, 16 Jun 2023, tip-bot2 for Lee Jones wrote:

> The following commit has been merged into the x86/urgent branch of tip:
> 
> Commit-ID:     d082d48737c75d2b3cc1f972b8c8674c25131534
> Gitweb:        https://git.kernel.org/tip/d082d48737c75d2b3cc1f972b8c8674c25131534
> Author:        Lee Jones <lee@kernel.org>
> AuthorDate:    Wed, 14 Jun 2023 17:38:54 +01:00
> Committer:     Dave Hansen <dave.hansen@linux.intel.com>
> CommitterDate: Fri, 16 Jun 2023 11:46:42 -07:00
> 
> x86/mm: Avoid using set_pgd() outside of real PGD pages
> 
> KPTI keeps around two PGDs: one for userspace and another for the
> kernel. Among other things, set_pgd() contains infrastructure to
> ensure that updates to the kernel PGD are reflected in the user PGD
> as well.
> 
> One side-effect of this is that set_pgd() expects to be passed whole
> pages.  Unfortunately, init_trampoline_kaslr() passes in a single entry:
> 'trampoline_pgd_entry'.
> 
> When KPTI is on, set_pgd() will update 'trampoline_pgd_entry' (an
> 8-Byte globally stored [.bss] variable) and will then proceed to
> replicate that value into the non-existent neighboring user page
> (located +4k away), leading to the corruption of other global [.bss]
> stored variables.
> 
> Fix it by directly assigning 'trampoline_pgd_entry' and avoiding
> set_pgd().
> 
> [ dhansen: tweak subject and changelog ]
> 
> Fixes: 0925dda5962e ("x86/mm/KASLR: Use only one PUD entry for real mode trampoline")
> Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
> Signed-off-by: Lee Jones <lee@kernel.org>
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: <stable@vger.kernel.org>
> Link: https://lore.kernel.org/all/20230614163859.924309-1-lee@kernel.org/g
> ---
>  arch/x86/mm/kaslr.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> index 557f0fe..37db264 100644
> --- a/arch/x86/mm/kaslr.c
> +++ b/arch/x86/mm/kaslr.c
> @@ -172,10 +172,10 @@ void __meminit init_trampoline_kaslr(void)
>  		set_p4d(p4d_tramp,
>  			__p4d(_KERNPG_TABLE | __pa(pud_page_tramp)));
>  
> -		set_pgd(&trampoline_pgd_entry,
> -			__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp)));
> +		trampoline_pgd_entry =
> +			__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp));
>  	} else {
> -		set_pgd(&trampoline_pgd_entry,
> -			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));
> +		trampoline_pgd_entry =
> +			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp));
>  	}
>  }

Could we have this expedited please?  There are users waiting for it.

Upstream commit is:

  d082d48737c75 ("x86/mm: Avoid using set_pgd() outside of real PGD pages")

Thanks muchly.

-- 
Lee Jones [李琼斯]

Re: [tip: x86/urgent] x86/mm: Avoid using set_pgd() outside of real PGD pages

[Greg KH]

On Mon, Jun 26, 2023 at 09:54:50AM +0100, Lee Jones wrote:
> Dear Stable,
> 
> On Fri, 16 Jun 2023, tip-bot2 for Lee Jones wrote:
> 
> > The following commit has been merged into the x86/urgent branch of tip:
> > 
> > Commit-ID:     d082d48737c75d2b3cc1f972b8c8674c25131534
> > Gitweb:        https://git.kernel.org/tip/d082d48737c75d2b3cc1f972b8c8674c25131534
> > Author:        Lee Jones <lee@kernel.org>
> > AuthorDate:    Wed, 14 Jun 2023 17:38:54 +01:00
> > Committer:     Dave Hansen <dave.hansen@linux.intel.com>
> > CommitterDate: Fri, 16 Jun 2023 11:46:42 -07:00
> > 
> > x86/mm: Avoid using set_pgd() outside of real PGD pages
> > 
> > KPTI keeps around two PGDs: one for userspace and another for the
> > kernel. Among other things, set_pgd() contains infrastructure to
> > ensure that updates to the kernel PGD are reflected in the user PGD
> > as well.
> > 
> > One side-effect of this is that set_pgd() expects to be passed whole
> > pages.  Unfortunately, init_trampoline_kaslr() passes in a single entry:
> > 'trampoline_pgd_entry'.
> > 
> > When KPTI is on, set_pgd() will update 'trampoline_pgd_entry' (an
> > 8-Byte globally stored [.bss] variable) and will then proceed to
> > replicate that value into the non-existent neighboring user page
> > (located +4k away), leading to the corruption of other global [.bss]
> > stored variables.
> > 
> > Fix it by directly assigning 'trampoline_pgd_entry' and avoiding
> > set_pgd().
> > 
> > [ dhansen: tweak subject and changelog ]
> > 
> > Fixes: 0925dda5962e ("x86/mm/KASLR: Use only one PUD entry for real mode trampoline")
> > Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
> > Signed-off-by: Lee Jones <lee@kernel.org>
> > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> > Cc: <stable@vger.kernel.org>
> > Link: https://lore.kernel.org/all/20230614163859.924309-1-lee@kernel.org/g
> > ---
> >  arch/x86/mm/kaslr.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> > index 557f0fe..37db264 100644
> > --- a/arch/x86/mm/kaslr.c
> > +++ b/arch/x86/mm/kaslr.c
> > @@ -172,10 +172,10 @@ void __meminit init_trampoline_kaslr(void)
> >  		set_p4d(p4d_tramp,
> >  			__p4d(_KERNPG_TABLE | __pa(pud_page_tramp)));
> >  
> > -		set_pgd(&trampoline_pgd_entry,
> > -			__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp)));
> > +		trampoline_pgd_entry =
> > +			__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp));
> >  	} else {
> > -		set_pgd(&trampoline_pgd_entry,
> > -			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));
> > +		trampoline_pgd_entry =
> > +			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp));
> >  	}
> >  }
> 
> Could we have this expedited please?  There are users waiting for it.
> 
> Upstream commit is:
> 
>   d082d48737c75 ("x86/mm: Avoid using set_pgd() outside of real PGD pages")

Please look through your emails you got this weekend, it's already
queued up in the following stable trees:
	queue-5.4 queue-5.10 queue-5.15 queue-6.1 queue-6.3

greg k-h

Re: [tip: x86/urgent] x86/mm: Avoid using set_pgd() outside of real PGD pages

[Lee Jones]

On Mon, 26 Jun 2023, Greg KH wrote:

> On Mon, Jun 26, 2023 at 09:54:50AM +0100, Lee Jones wrote:
> > Dear Stable,
> > 
> > On Fri, 16 Jun 2023, tip-bot2 for Lee Jones wrote:
> > 
> > > The following commit has been merged into the x86/urgent branch of tip:
> > > 
> > > Commit-ID:     d082d48737c75d2b3cc1f972b8c8674c25131534
> > > Gitweb:        https://git.kernel.org/tip/d082d48737c75d2b3cc1f972b8c8674c25131534
> > > Author:        Lee Jones <lee@kernel.org>
> > > AuthorDate:    Wed, 14 Jun 2023 17:38:54 +01:00
> > > Committer:     Dave Hansen <dave.hansen@linux.intel.com>
> > > CommitterDate: Fri, 16 Jun 2023 11:46:42 -07:00
> > > 
> > > x86/mm: Avoid using set_pgd() outside of real PGD pages
> > > 
> > > KPTI keeps around two PGDs: one for userspace and another for the
> > > kernel. Among other things, set_pgd() contains infrastructure to
> > > ensure that updates to the kernel PGD are reflected in the user PGD
> > > as well.
> > > 
> > > One side-effect of this is that set_pgd() expects to be passed whole
> > > pages.  Unfortunately, init_trampoline_kaslr() passes in a single entry:
> > > 'trampoline_pgd_entry'.
> > > 
> > > When KPTI is on, set_pgd() will update 'trampoline_pgd_entry' (an
> > > 8-Byte globally stored [.bss] variable) and will then proceed to
> > > replicate that value into the non-existent neighboring user page
> > > (located +4k away), leading to the corruption of other global [.bss]
> > > stored variables.
> > > 
> > > Fix it by directly assigning 'trampoline_pgd_entry' and avoiding
> > > set_pgd().
> > > 
> > > [ dhansen: tweak subject and changelog ]
> > > 
> > > Fixes: 0925dda5962e ("x86/mm/KASLR: Use only one PUD entry for real mode trampoline")
> > > Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
> > > Signed-off-by: Lee Jones <lee@kernel.org>
> > > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> > > Cc: <stable@vger.kernel.org>
> > > Link: https://lore.kernel.org/all/20230614163859.924309-1-lee@kernel.org/g
> > > ---
> > >  arch/x86/mm/kaslr.c | 8 ++++----
> > >  1 file changed, 4 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> > > index 557f0fe..37db264 100644
> > > --- a/arch/x86/mm/kaslr.c
> > > +++ b/arch/x86/mm/kaslr.c
> > > @@ -172,10 +172,10 @@ void __meminit init_trampoline_kaslr(void)
> > >  		set_p4d(p4d_tramp,
> > >  			__p4d(_KERNPG_TABLE | __pa(pud_page_tramp)));
> > >  
> > > -		set_pgd(&trampoline_pgd_entry,
> > > -			__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp)));
> > > +		trampoline_pgd_entry =
> > > +			__pgd(_KERNPG_TABLE | __pa(p4d_page_tramp));
> > >  	} else {
> > > -		set_pgd(&trampoline_pgd_entry,
> > > -			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));
> > > +		trampoline_pgd_entry =
> > > +			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp));
> > >  	}
> > >  }
> > 
> > Could we have this expedited please?  There are users waiting for it.
> > 
> > Upstream commit is:
> > 
> >   d082d48737c75 ("x86/mm: Avoid using set_pgd() outside of real PGD pages")
> 
> Please look through your emails you got this weekend, it's already
> queued up in the following stable trees:
> 	queue-5.4 queue-5.10 queue-5.15 queue-6.1 queue-6.3

Haven't reached those ones yet - only 160 to go!

Thank you though, very much appreciated.

-- 
Lee Jones [李琼斯]