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mm/execmem: Unify early execmem_cache behaviour

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Early kernel memory is RWX, only at the end of early boot (before SMP)
do we mark things ROX. Have execmem_cache mirror this behaviour for
early users.

This avoids having to remember what code is execmem and what is not --
we can poke everything with impunity ;-) Also performance for not
having to do endless text_poke_mm switches.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
This commit is contained in:
Peter Zijlstra 2025-04-23 16:30:11 +02:00 • committed by Dave Hansen
parent f0cd7091cc
commit d6d1e3e658
4 changed files with 50 additions and 4 deletions
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3
arch/x86/mm/init_32.c
View file

@ -30,6 +30,7 @@
#include <linux/initrd.h>
#include <linux/cpumask.h>
#include <linux/gfp.h>
#include <linux/execmem.h>
#include <asm/asm.h>
#include <asm/bios_ebda.h>
@ -755,6 +756,8 @@ void mark_rodata_ro(void)
pr_info("Write protecting kernel text and read-only data: %luk\n",
size >> 10);
execmem_cache_make_ro();
kernel_set_to_readonly = 1;
#ifdef CONFIG_CPA_DEBUG

3
arch/x86/mm/init_64.c
View file

@ -34,6 +34,7 @@
#include <linux/gfp.h>
#include <linux/kcore.h>
#include <linux/bootmem_info.h>
#include <linux/execmem.h>
#include <asm/processor.h>
#include <asm/bios_ebda.h>
@ -1391,6 +1392,8 @@ void mark_rodata_ro(void)
(end - start) >> 10);
set_memory_ro(start, (end - start) >> PAGE_SHIFT);
execmem_cache_make_ro();
kernel_set_to_readonly = 1;
/*

8
include/linux/execmem.h
View file

@ -53,7 +53,7 @@ enum execmem_range_flags {
EXECMEM_ROX_CACHE = (1 << 1),
};
#ifdef CONFIG_ARCH_HAS_EXECMEM_ROX
#if defined(CONFIG_ARCH_HAS_EXECMEM_ROX) && defined(CONFIG_EXECMEM)
/**
* execmem_fill_trapping_insns - set memory to contain instructions that
* will trap
@ -93,9 +93,15 @@ int execmem_make_temp_rw(void *ptr, size_t size);
* Return: 0 on success or negative error code on failure.
*/
int execmem_restore_rox(void *ptr, size_t size);
/*
* Called from mark_readonly(), where the system transitions to ROX.
*/
void execmem_cache_make_ro(void);
#else
static inline int execmem_make_temp_rw(void *ptr, size_t size) { return 0; }
static inline int execmem_restore_rox(void *ptr, size_t size) { return 0; }
static inline void execmem_cache_make_ro(void) { }
#endif
/**

40
mm/execmem.c
View file

@ -254,6 +254,34 @@ out_unlock:
return ptr;
}
static bool execmem_cache_rox = false;
void execmem_cache_make_ro(void)
{
struct maple_tree *free_areas = &execmem_cache.free_areas;
struct maple_tree *busy_areas = &execmem_cache.busy_areas;
MA_STATE(mas_free, free_areas, 0, ULONG_MAX);
MA_STATE(mas_busy, busy_areas, 0, ULONG_MAX);
struct mutex *mutex = &execmem_cache.mutex;
void *area;
execmem_cache_rox = true;
mutex_lock(mutex);
mas_for_each(&mas_free, area, ULONG_MAX) {
unsigned long pages = mas_range_len(&mas_free) >> PAGE_SHIFT;
set_memory_ro(mas_free.index, pages);
}
mas_for_each(&mas_busy, area, ULONG_MAX) {
unsigned long pages = mas_range_len(&mas_busy) >> PAGE_SHIFT;
set_memory_ro(mas_busy.index, pages);
}
mutex_unlock(mutex);
}
static int execmem_cache_populate(struct execmem_range *range, size_t size)
{
unsigned long vm_flags = VM_ALLOW_HUGE_VMAP;
@ -274,9 +302,15 @@ static int execmem_cache_populate(struct execmem_range *range, size_t size)
/* fill memory with instructions that will trap */
execmem_fill_trapping_insns(p, alloc_size, /* writable = */ true);
err = set_memory_rox((unsigned long)p, vm->nr_pages);
if (err)
goto err_free_mem;
if (execmem_cache_rox) {
err = set_memory_rox((unsigned long)p, vm->nr_pages);
if (err)
goto err_free_mem;
} else {
err = set_memory_x((unsigned long)p, vm->nr_pages);
if (err)
goto err_free_mem;
}
err = execmem_cache_add(p, alloc_size);
if (err)