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ANDROID: 16K: Reduce mmap rand bits

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The emulated page size in userspace is larger than the kernel page size.
This means that the kernel can no longer provide the max amount of mmap
rand bits as before. The maximum must be reduced by the difference
between the emulated page shift and the real page shift. This is only
necessary for the 64-bit case and not for the compat (32-bit) case.

Also move initialization of mmap_rnd_bits_* globals to
init_mmap_rnd_bits(), which is called at core_init time. This is
necessary since the values are no longer build time constants.

Bug: 383389337
Bug: 315325080
Bug: 302403436
Change-Id: I0f45a9f40b4f4cd06e98e0bfa62732c5d70056be
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
This commit is contained in:
Kalesh Singh
2024-02-06 22:33:30 -08:00
committed by Carlos Llamas
parent 80e2a42d97
commit 796be8fd27
3 changed files with 23 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/mm.h
View File

@@ -90,13 +90,13 @@ extern int sysctl_legacy_va_layout;
#endif
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
extern const int mmap_rnd_bits_min;
extern int mmap_rnd_bits_min __ro_after_init;
extern int mmap_rnd_bits_max __ro_after_init;
extern int mmap_rnd_bits __read_mostly;
#endif
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
extern const int mmap_rnd_compat_bits_min;
extern const int mmap_rnd_compat_bits_max;
extern int mmap_rnd_compat_bits_min __ro_after_init;
extern int mmap_rnd_compat_bits_max __ro_after_init;
extern int mmap_rnd_compat_bits __read_mostly;
#endif

6
mm/mmap.c
View File

@@ -66,13 +66,13 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(vm_unmapped_area);
#endif
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
const int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
int mmap_rnd_bits_min __ro_after_init = CONFIG_ARCH_MMAP_RND_BITS_MIN;
int mmap_rnd_bits_max __ro_after_init = CONFIG_ARCH_MMAP_RND_BITS_MAX;
int mmap_rnd_bits __read_mostly = CONFIG_ARCH_MMAP_RND_BITS;
#endif
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
const int mmap_rnd_compat_bits_min = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN;
const int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX;
int mmap_rnd_compat_bits_min __ro_after_init = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN;
int mmap_rnd_compat_bits_max __ro_after_init = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX;
int mmap_rnd_compat_bits __read_mostly = CONFIG_ARCH_MMAP_RND_COMPAT_BITS;
#endif

17
mm/page_size_compat.c
View File

@@ -9,10 +9,12 @@
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/kstrtox.h>
#include <linux/mm.h>
#include <linux/page_size_compat.h>
#define MIN_PAGE_SHIFT_COMPAT (PAGE_SHIFT + 1)
#define MAX_PAGE_SHIFT_COMPAT 16 /* Max of 64KB */
#define __MMAP_RND_BITS(x) (x - (__PAGE_SHIFT - PAGE_SHIFT))
DEFINE_STATIC_KEY_FALSE(page_shift_compat_enabled);
@@ -39,3 +41,18 @@ static int __init early_page_shift_compat(char *buf)
return 0;
}
early_param("androidboot.page_shift", early_page_shift_compat);
static int __init init_mmap_rnd_bits(void)
{
if (!static_branch_unlikely(&page_shift_compat_enabled))
return 0;
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
mmap_rnd_bits_min = __MMAP_RND_BITS(CONFIG_ARCH_MMAP_RND_BITS_MIN);
mmap_rnd_bits_max = __MMAP_RND_BITS(CONFIG_ARCH_MMAP_RND_BITS_MAX);
mmap_rnd_bits = __MMAP_RND_BITS(CONFIG_ARCH_MMAP_RND_BITS);
#endif
return 0;
}
core_initcall(init_mmap_rnd_bits);