* [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned
@ 2016-01-22 18:13 Alexander Kuleshov
2016-01-23 1:42 ` Brian Gerst
0 siblings, 1 reply; 3+ messages in thread
From: Alexander Kuleshov @ 2016-01-22 18:13 UTC (permalink / raw)
To: Thomas Gleixner
Cc: Ingo Molnar, H . Peter Anvin, Andy Lutomirski, Borislav Petkov,
Denys Vlasenko, Andrey Ryabinin, x86, linux-kernel,
Alexander Kuleshov
We check that the base address of the kernel is 2M aligned in
the arch/x86/kernel/head_65.S right after jump to the decompressed
kernel. But we already have a check in the decompress_kernel()
which validates that kernel location is MIN_KERNEL_ALIGN aligned
which is 2M too for x86_64.
Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
---
arch/x86/kernel/head_64.S | 6 ------
1 file changed, 6 deletions(-)
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index ffdc0e8..4967cba 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -75,12 +75,6 @@ startup_64:
leaq _text(%rip), %rbp
subq $_text - __START_KERNEL_map, %rbp
- /* Is the address not 2M aligned? */
- movq %rbp, %rax
- andl $~PMD_PAGE_MASK, %eax
- testl %eax, %eax
- jnz bad_address
-
/*
* Is the address too large?
*/
--
2.7.0.25.gfc10eb5
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned
2016-01-22 18:13 [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned Alexander Kuleshov
@ 2016-01-23 1:42 ` Brian Gerst
2016-01-23 6:37 ` Alexander Kuleshov
0 siblings, 1 reply; 3+ messages in thread
From: Brian Gerst @ 2016-01-23 1:42 UTC (permalink / raw)
To: Alexander Kuleshov
Cc: Thomas Gleixner, Ingo Molnar, H . Peter Anvin, Andy Lutomirski,
Borislav Petkov, Denys Vlasenko, Andrey Ryabinin,
the arch/x86 maintainers, Linux Kernel Mailing List
On Fri, Jan 22, 2016 at 1:13 PM, Alexander Kuleshov
<kuleshovmail@gmail.com> wrote:
> We check that the base address of the kernel is 2M aligned in
> the arch/x86/kernel/head_65.S right after jump to the decompressed
> kernel. But we already have a check in the decompress_kernel()
> which validates that kernel location is MIN_KERNEL_ALIGN aligned
> which is 2M too for x86_64.
>
> Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
> ---
> arch/x86/kernel/head_64.S | 6 ------
> 1 file changed, 6 deletions(-)
>
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index ffdc0e8..4967cba 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -75,12 +75,6 @@ startup_64:
> leaq _text(%rip), %rbp
> subq $_text - __START_KERNEL_map, %rbp
>
> - /* Is the address not 2M aligned? */
> - movq %rbp, %rax
> - andl $~PMD_PAGE_MASK, %eax
> - testl %eax, %eax
> - jnz bad_address
> -
> /*
> * Is the address too large?
> */
I think we still need to do the check, in case we came from a 64-bit
bootloader that directly jumped to startup_64. However, this check
can be simplified to:
testl $~PMD_PAGE_MASK, %ebp
jnz bad_address
--
Brian Gerst
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned
2016-01-23 1:42 ` Brian Gerst
@ 2016-01-23 6:37 ` Alexander Kuleshov
0 siblings, 0 replies; 3+ messages in thread
From: Alexander Kuleshov @ 2016-01-23 6:37 UTC (permalink / raw)
To: Brian Gerst
Cc: Alexander Kuleshov, Thomas Gleixner, Ingo Molnar, H . Peter Anvin,
Andy Lutomirski, Borislav Petkov, Denys Vlasenko, Andrey Ryabinin,
the arch/x86 maintainers, Linux Kernel Mailing List
Hello Brian,
On 01-22-16, Brian Gerst wrote:
> >
> > - /* Is the address not 2M aligned? */
> > - movq %rbp, %rax
> > - andl $~PMD_PAGE_MASK, %eax
> > - testl %eax, %eax
> > - jnz bad_address
> > -
> > /*
> > * Is the address too large?
> > */
>
> I think we still need to do the check, in case we came from a 64-bit
> bootloader that directly jumped to startup_64. However, this check
> can be simplified to:
>
> testl $~PMD_PAGE_MASK, %ebp
> jnz bad_address
Ah, ok, in this way we can't trust a bootloader. I just thought that
64-bit entry point is startup_64 from arch/x86/boot/compressed/head_64.S
Thank you.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2016-01-22 18:13 [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned Alexander Kuleshov
2016-01-23 1:42 ` Brian Gerst
2016-01-23 6:37 ` Alexander Kuleshov
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