[PATCH] arm64: fix rodata=full again

[PATCH] arm64: fix rodata=full again

[Ard Biesheuvel]

Commit 2e8cff0a0eee87b2 ("arm64: fix rodata=full") addressed a couple of
issues with the rodata= kernel command line option, which is not a
simple boolean on arm64, and inadvertently got broken due to changes in
the generic bool handling.

Unfortunately, the resulting code never clears the rodata_full boolean
variable if it defaults to true and rodata=on or rodata=off is passed,
as the generic code is not aware of the existence of this variable.

Given the way this code is plumbed together, clearing rodata_full when
returning false from arch_parse_debug_rodata() may result in
inconsistencies if the generic code decides that it cannot parse the
right hand side, so the best way to deal with this is to only take
rodata_full in account if rodata_enabled is also true.

Fixes: 2e8cff0a0eee87b2 ("arm64: fix rodata=full")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/mm/pageattr.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index d107c3d434e22455..5922178d7a064c1c 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -26,7 +26,7 @@ bool can_set_direct_map(void)
 	 * mapped at page granularity, so that it is possible to
 	 * protect/unprotect single pages.
 	 */
-	return rodata_full || debug_pagealloc_enabled() ||
+	return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
 		IS_ENABLED(CONFIG_KFENCE);
 }
 
@@ -102,7 +102,8 @@ static int change_memory_common(unsigned long addr, int numpages,
 	 * If we are manipulating read-only permissions, apply the same
 	 * change to the linear mapping of the pages that back this VM area.
 	 */
-	if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
+	if (rodata_enabled &&
+	    rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
 			    pgprot_val(clear_mask) == PTE_RDONLY)) {
 		for (i = 0; i < area->nr_pages; i++) {
 			__change_memory_common((u64)page_address(area->pages[i]),
-- 
2.35.1


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Re: [PATCH] arm64: fix rodata=full again

[Will Deacon]

On Thu, Nov 03, 2022 at 06:00:15PM +0100, Ard Biesheuvel wrote:
> Commit 2e8cff0a0eee87b2 ("arm64: fix rodata=full") addressed a couple of
> issues with the rodata= kernel command line option, which is not a
> simple boolean on arm64, and inadvertently got broken due to changes in
> the generic bool handling.
> 
> Unfortunately, the resulting code never clears the rodata_full boolean
> variable if it defaults to true and rodata=on or rodata=off is passed,
> as the generic code is not aware of the existence of this variable.
> 
> Given the way this code is plumbed together, clearing rodata_full when
> returning false from arch_parse_debug_rodata() may result in
> inconsistencies if the generic code decides that it cannot parse the
> right hand side, so the best way to deal with this is to only take
> rodata_full in account if rodata_enabled is also true.
> 
> Fixes: 2e8cff0a0eee87b2 ("arm64: fix rodata=full")
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  arch/arm64/mm/pageattr.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index d107c3d434e22455..5922178d7a064c1c 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -26,7 +26,7 @@ bool can_set_direct_map(void)
>  	 * mapped at page granularity, so that it is possible to
>  	 * protect/unprotect single pages.
>  	 */
> -	return rodata_full || debug_pagealloc_enabled() ||
> +	return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
>  		IS_ENABLED(CONFIG_KFENCE);
>  }
>  
> @@ -102,7 +102,8 @@ static int change_memory_common(unsigned long addr, int numpages,
>  	 * If we are manipulating read-only permissions, apply the same
>  	 * change to the linear mapping of the pages that back this VM area.
>  	 */
> -	if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
> +	if (rodata_enabled &&
> +	    rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
>  			    pgprot_val(clear_mask) == PTE_RDONLY)) {
>  		for (i = 0; i < area->nr_pages; i++) {
>  			__change_memory_common((u64)page_address(area->pages[i]),
> -- 
> 2.35.1

Hmm, I dislike how error-prone this is, but thanks for the fix:

Acked-by: Will Deacon <will@kernel.org>

Will

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Re: [PATCH] arm64: fix rodata=full again

[Catalin Marinas]

On Thu, 3 Nov 2022 18:00:15 +0100, Ard Biesheuvel wrote:
> Commit 2e8cff0a0eee87b2 ("arm64: fix rodata=full") addressed a couple of
> issues with the rodata= kernel command line option, which is not a
> simple boolean on arm64, and inadvertently got broken due to changes in
> the generic bool handling.
> 
> Unfortunately, the resulting code never clears the rodata_full boolean
> variable if it defaults to true and rodata=on or rodata=off is passed,
> as the generic code is not aware of the existence of this variable.
> 
> [...]

Applied to arm64 (for-next/fixes), thanks!

[1/1] arm64: fix rodata=full again
      https://git.kernel.org/arm64/c/2081b3bd0c11

-- 
Catalin


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