Re: [RFC PATCH 4/9] module: Allocate MOD_INIT_TEXT from the MOD_TEXT ROX allocation

[Bradley Morgan <brads@mainlining.org>]

On 22 August 2026 14:53:26 BST, Ard Biesheuvel <ardb+git@google.com> wrote:
>From: Ard Biesheuvel <ardb@kernel.org>
>
>When execmem ROX caches are used for module text and inittext, place
>them adjacently in memory, by allocating space for both initially, and
>splitting off the space for MOD_INIT_TEXT as needed.
>
>This avoids the corner case on arm64, where .init.text being placed far
>from .text results in a lot of complexity wrt indirect branches and PLTs
>that we'd prefer to avoid.
>

I can't see anything wrong, thanks for the patch

Reviewed-by: Bradley Morgan <brads@mainlining.org> # kernel/

>Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>---
> kernel/module/main.c | 22 ++++++++++++++++----
> 1 file changed, 18 insertions(+), 4 deletions(-)
>
>diff --git a/kernel/module/main.c b/kernel/module/main.c
>index 46dd8d25a605..2d6213496359 100644
>--- a/kernel/module/main.c
>+++ b/kernel/module/main.c
>@@ -1342,7 +1342,7 @@ static int module_memory_alloc(struct module *mod, enum mod_mem_type type)
> {
> 	unsigned int size = PAGE_ALIGN(mod->mem[type].size);
> 	enum execmem_type execmem_type;
>-	void *ptr;
>+	void *ptr = NULL;
> 
> 	mod->mem[type].size = size;
> 
>@@ -1351,11 +1351,25 @@ static int module_memory_alloc(struct module *mod, enum mod_mem_type type)
> 	else
> 		execmem_type = EXECMEM_MODULE_TEXT;
> 
>-	ptr = execmem_alloc_rw(execmem_type, size);
>+	bool is_rox = execmem_is_rox(execmem_type);
>+	if (is_rox) {
>+		/*
>+		 * Special case for MOD_TEXT / MOD_INIT_TEXT: allocate the
>+		 * latter by splitting off required space from the former
>+		 * so that they are always placed close together.
>+		 */
>+		if (type == MOD_TEXT)
>+			size += PAGE_ALIGN(mod->mem[MOD_INIT_TEXT].size);
>+		else if (type == MOD_INIT_TEXT)
>+			ptr = execmem_split(mod->mem[MOD_TEXT].base, size);
>+	}
>+
>+	if (!ptr)
>+		ptr = execmem_alloc_rw(execmem_type, size);
> 	if (!ptr)
> 		return -ENOMEM;
> 
>-	mod->mem[type].is_rox = execmem_is_rox(execmem_type);
>+	mod->mem[type].is_rox = is_rox;
> 
> 	/*
> 	 * The pointer to these blocks of memory are stored on the module
>@@ -1368,7 +1382,7 @@ static int module_memory_alloc(struct module *mod, enum mod_mem_type type)
> 	 * *do* eventually get freed, but let's just keep things simple
> 	 * and avoid *any* false positives.
> 	 */
>-	if (!mod->mem[type].is_rox)
>+	if (!is_rox)
> 		kmemleak_not_leak(ptr);
> 
> 	memset(ptr, 0, size);
>


--- Thanks!
https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/