diff mbox series

[v4,02/26] x86/build: Remove RWX sections and align on 4KB

Message ID 721b5c42e0e79d307d5bcb08f9c8402f5067ded0.1671098103.git.baskov@ispras.ru
State New
Headers
Series x86_64: Improvements at compressed kernel stage |

Commit Message

Evgeniy Baskov Dec. 15, 2022, 12:37 p.m. UTC 
  Avoid creating sections simultaneously writable and readable
to prepare for W^X implementation. Align sections on page size (4KB) to
allow protecting them in the page tables.

Split init code form ".init" segment into separate R_X ".inittext"
segment and make ".init" segment non-executable.

Also add these segments to x86_32 architecture for consistency.
Currently paging is disabled in x86_32 in compressed kernel, so
protection is not applied anyways, but .init code was incorrectly
placed in non-executable ".data" segment. This should not change
anything meaningful in memory layout now, but might be required in case
memory protection will also be implemented in compressed kernel for
x86_32.

Tested-by: Mario Limonciello <mario.limonciello@amd.com>
Tested-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>
---
 arch/x86/kernel/vmlinux.lds.S | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

Comments

Ard Biesheuvel March 10, 2023, 2:45 p.m. UTC | #1 
On Thu, 15 Dec 2022 at 13:38, Evgeniy Baskov <baskov@ispras.ru> wrote:
>
> Avoid creating sections simultaneously writable and readable
> to prepare for W^X implementation. Align sections on page size (4KB) to
> allow protecting them in the page tables.
>
> Split init code form ".init" segment into separate R_X ".inittext"
> segment and make ".init" segment non-executable.
>
> Also add these segments to x86_32 architecture for consistency.
> Currently paging is disabled in x86_32 in compressed kernel, so
> protection is not applied anyways, but .init code was incorrectly
> placed in non-executable ".data" segment. This should not change
> anything meaningful in memory layout now, but might be required in case
> memory protection will also be implemented in compressed kernel for
> x86_32.
>
> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
> Tested-by: Peter Jones <pjones@redhat.com>
> Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

One nit: the series modifies both the decompressor linker script and
the core kernel one, so please make it very explicit in the commit log
which one is being modified, and why it matters for this particular
context.


> ---
>  arch/x86/kernel/vmlinux.lds.S | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 2e0ee14229bf..2e56d694c491 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -102,12 +102,11 @@ jiffies = jiffies_64;
>  PHDRS {
>         text PT_LOAD FLAGS(5);          /* R_E */
>         data PT_LOAD FLAGS(6);          /* RW_ */
> -#ifdef CONFIG_X86_64
> -#ifdef CONFIG_SMP
> +#if defined(CONFIG_X86_64) && defined(CONFIG_SMP)
>         percpu PT_LOAD FLAGS(6);        /* RW_ */
>  #endif
> -       init PT_LOAD FLAGS(7);          /* RWE */
> -#endif
> +       inittext PT_LOAD FLAGS(5);      /* R_E */
> +       init PT_LOAD FLAGS(6);          /* RW_ */
>         note PT_NOTE FLAGS(0);          /* ___ */
>  }
>
> @@ -227,9 +226,10 @@ SECTIONS
>  #endif
>
>         INIT_TEXT_SECTION(PAGE_SIZE)
> -#ifdef CONFIG_X86_64
> -       :init
> -#endif
> +       :inittext
> +
> +       . = ALIGN(PAGE_SIZE);
> +
>
>         /*
>          * Section for code used exclusively before alternatives are run. All
> @@ -241,6 +241,7 @@ SECTIONS
>         .altinstr_aux : AT(ADDR(.altinstr_aux) - LOAD_OFFSET) {
>                 *(.altinstr_aux)
>         }
> +       :init
>
>         INIT_DATA_SECTION(16)
>
> --
> 2.37.4
>
Evgeniy Baskov March 11, 2023, 2:31 p.m. UTC | #2 
On 2023-03-10 17:45, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:38, Evgeniy Baskov <baskov@ispras.ru> wrote:
>> 
>> Avoid creating sections simultaneously writable and readable
>> to prepare for W^X implementation. Align sections on page size (4KB) 
>> to
>> allow protecting them in the page tables.
>> 
>> Split init code form ".init" segment into separate R_X ".inittext"
>> segment and make ".init" segment non-executable.
>> 
>> Also add these segments to x86_32 architecture for consistency.
>> Currently paging is disabled in x86_32 in compressed kernel, so
>> protection is not applied anyways, but .init code was incorrectly
>> placed in non-executable ".data" segment. This should not change
>> anything meaningful in memory layout now, but might be required in 
>> case
>> memory protection will also be implemented in compressed kernel for
>> x86_32.
>> 
>> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
>> Tested-by: Peter Jones <pjones@redhat.com>
>> Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>
> 
> Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
> 
> One nit: the series modifies both the decompressor linker script and
> the core kernel one, so please make it very explicit in the commit log
> which one is being modified, and why it matters for this particular
> context.
> 

Thanks! I'll amend the log.
> 
>> ---
>>  arch/x86/kernel/vmlinux.lds.S | 15 ++++++++-------
>>  1 file changed, 8 insertions(+), 7 deletions(-)
>> 
>> diff --git a/arch/x86/kernel/vmlinux.lds.S 
>> b/arch/x86/kernel/vmlinux.lds.S
>> index 2e0ee14229bf..2e56d694c491 100644
>> --- a/arch/x86/kernel/vmlinux.lds.S
>> +++ b/arch/x86/kernel/vmlinux.lds.S
>> @@ -102,12 +102,11 @@ jiffies = jiffies_64;
>>  PHDRS {
>>         text PT_LOAD FLAGS(5);          /* R_E */
>>         data PT_LOAD FLAGS(6);          /* RW_ */
>> -#ifdef CONFIG_X86_64
>> -#ifdef CONFIG_SMP
>> +#if defined(CONFIG_X86_64) && defined(CONFIG_SMP)
>>         percpu PT_LOAD FLAGS(6);        /* RW_ */
>>  #endif
>> -       init PT_LOAD FLAGS(7);          /* RWE */
>> -#endif
>> +       inittext PT_LOAD FLAGS(5);      /* R_E */
>> +       init PT_LOAD FLAGS(6);          /* RW_ */
>>         note PT_NOTE FLAGS(0);          /* ___ */
>>  }
>> 
>> @@ -227,9 +226,10 @@ SECTIONS
>>  #endif
>> 
>>         INIT_TEXT_SECTION(PAGE_SIZE)
>> -#ifdef CONFIG_X86_64
>> -       :init
>> -#endif
>> +       :inittext
>> +
>> +       . = ALIGN(PAGE_SIZE);
>> +
>> 
>>         /*
>>          * Section for code used exclusively before alternatives are 
>> run. All
>> @@ -241,6 +241,7 @@ SECTIONS
>>         .altinstr_aux : AT(ADDR(.altinstr_aux) - LOAD_OFFSET) {
>>                 *(.altinstr_aux)
>>         }
>> +       :init
>> 
>>         INIT_DATA_SECTION(16)
>> 
>> --
>> 2.37.4
>>
diff mbox series

Patch

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 2e0ee14229bf..2e56d694c491 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -102,12 +102,11 @@  jiffies = jiffies_64;
 PHDRS {
 	text PT_LOAD FLAGS(5);          /* R_E */
 	data PT_LOAD FLAGS(6);          /* RW_ */
-#ifdef CONFIG_X86_64
-#ifdef CONFIG_SMP
+#if defined(CONFIG_X86_64) && defined(CONFIG_SMP)
 	percpu PT_LOAD FLAGS(6);        /* RW_ */
 #endif
-	init PT_LOAD FLAGS(7);          /* RWE */
-#endif
+	inittext PT_LOAD FLAGS(5);      /* R_E */
+	init PT_LOAD FLAGS(6);          /* RW_ */
 	note PT_NOTE FLAGS(0);          /* ___ */
 }
 
@@ -227,9 +226,10 @@  SECTIONS
 #endif
 
 	INIT_TEXT_SECTION(PAGE_SIZE)
-#ifdef CONFIG_X86_64
-	:init
-#endif
+	:inittext
+
+	. = ALIGN(PAGE_SIZE);
+
 
 	/*
 	 * Section for code used exclusively before alternatives are run. All
@@ -241,6 +241,7 @@  SECTIONS
 	.altinstr_aux : AT(ADDR(.altinstr_aux) - LOAD_OFFSET) {
 		*(.altinstr_aux)
 	}
+	:init
 
 	INIT_DATA_SECTION(16)