From: Xiongwei Song <sxwjean@xxxxxxxxx>
The code logic of arch_pick_mmap_layout() of x86 is basiclly same as
arch_pick_mmap_layout() where is in mm/util.c. Let's enable
ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT for x86 to use generic
arch_pick_mmap_layout(). Meanwhile, delete the arch_pick_mmap_layout()
and the related assistant functions in x86.
To verify if the entropy of mmap is kept after the patch, I did basically
test with the following c code:
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
int main(int argc, char *argv[])
{
unsigned long *addr;
addr = mmap(NULL, 4096, PROT_READ, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
if (addr == MAP_FAILED) {
printf("NULL\n");
} else {
printf("%lx\n", (unsigned long)addr);
munmap(addr, 4096);
}
return 0;
}
Run the program above 10 thousands times to get the mmap address, please
see the results below.
Before this patch:
Virtual Address Range | hit times
----------------------------------------
0x7f0000000000 - 0x7f0ffffff000 | 655
0x7f1000000000 - 0x7f1ffffff000 | 617
0x7f2000000000 - 0x7f2ffffff000 | 636
0x7f3000000000 - 0x7f3ffffff000 | 625
0x7f4000000000 - 0x7f4ffffff000 | 651
0x7f5000000000 - 0x7f5ffffff000 | 591
0x7f6000000000 - 0x7f6ffffff000 | 623
0x7f7000000000 - 0x7f7ffffff000 | 627
0x7f8000000000 - 0x7f8ffffff000 | 638
0x7f9000000000 - 0x7f9ffffff000 | 586
0x7fa000000000 - 0x7faffffff000 | 637
0x7fb000000000 - 0x7fbffffff000 | 607
0x7fc000000000 - 0x7fcffffff000 | 618
0x7fd000000000 - 0x7fdffffff000 | 656
0x7fe000000000 - 0x7feffffff000 | 614
0x7ff000000000 - 0x7ffffffff000 | 619
After this patch:
Virtual Address Range | hit times
----------------------------------------
0x7f0000000000 - 0x7f0ffffff000 | 661
0x7f1000000000 - 0x7f1ffffff000 | 645
0x7f2000000000 - 0x7f2ffffff000 | 609
0x7f3000000000 - 0x7f3ffffff000 | 594
0x7f4000000000 - 0x7f4ffffff000 | 616
0x7f5000000000 - 0x7f5ffffff000 | 622
0x7f6000000000 - 0x7f6ffffff000 | 617
0x7f7000000000 - 0x7f7ffffff000 | 582
0x7f8000000000 - 0x7f8ffffff000 | 618
0x7f9000000000 - 0x7f9ffffff000 | 629
0x7fa000000000 - 0x7faffffff000 | 635
0x7fb000000000 - 0x7fbffffff000 | 625
0x7fc000000000 - 0x7fcffffff000 | 614
0x7fd000000000 - 0x7fdffffff000 | 610
0x7fe000000000 - 0x7feffffff000 | 648
0x7ff000000000 - 0x7ffffffff000 | 675
It looks like the result after the patch is reasonable.
Furthermore, define a is_compat_task() for x86 to fix function undefined
issue.
Add __weak attribute to generic arch_randomize_brk() to ensure the kernel
always uses the arch_randomize_brk() of x86 in x86 arch.
Signed-off-by: Xiongwei Song <sxwjean@xxxxxxxxx>
---
arch/x86/Kconfig | 1 +
arch/x86/include/asm/compat.h | 5 ++
arch/x86/mm/mmap.c | 112 ----------------------------------
mm/util.c | 2 +-
4 files changed, 7 insertions(+), 113 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a52e81cb256e..01a40b710103 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -114,6 +114,7 @@ config X86
select ARCH_USE_SYM_ANNOTATIONS
select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
select ARCH_WANT_DEFAULT_BPF_JIT if X86_64
+ select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
select ARCH_WANTS_DYNAMIC_TASK_STRUCT
select ARCH_WANTS_NO_INSTR
select ARCH_WANT_HUGE_PMD_SHARE
diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
index 7516e4199b3c..22714a202794 100644
--- a/arch/x86/include/asm/compat.h
+++ b/arch/x86/include/asm/compat.h
@@ -156,6 +156,11 @@ struct compat_shmid64_ds {
(!!(task_pt_regs(current)->orig_ax & __X32_SYSCALL_BIT))
#endif
+static inline int is_compat_task(void)
+{
+ return IS_ENABLED(CONFIG_COMPAT) && test_thread_flag(TIF_ADDR32);
+}
+
static inline bool in_x32_syscall(void)
{
#ifdef CONFIG_X86_X32_ABI
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index c90c20904a60..daf65cc5e5b1 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -38,118 +38,6 @@ unsigned long task_size_64bit(int full_addr_space)
return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW;
}
-static unsigned long stack_maxrandom_size(unsigned long task_size)
-{
- unsigned long max = 0;
- if (current->flags & PF_RANDOMIZE) {
- max = (-1UL) & __STACK_RND_MASK(task_size == task_size_32bit());
- max <<= PAGE_SHIFT;
- }
-
- return max;
-}
-
-#ifdef CONFIG_COMPAT
-# define mmap32_rnd_bits mmap_rnd_compat_bits
-# define mmap64_rnd_bits mmap_rnd_bits
-#else
-# define mmap32_rnd_bits mmap_rnd_bits
-# define mmap64_rnd_bits mmap_rnd_bits
-#endif
-
-#define SIZE_128M (128 * 1024 * 1024UL)
-
-static int mmap_is_legacy(void)
-{
- if (current->personality & ADDR_COMPAT_LAYOUT)
- return 1;
-
- return sysctl_legacy_va_layout;
-}
-
-static unsigned long arch_rnd(unsigned int rndbits)
-{
- if (!(current->flags & PF_RANDOMIZE))
- return 0;
- return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
-}
-
-unsigned long arch_mmap_rnd(void)
-{
- return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
-}
-
-static unsigned long mmap_base(unsigned long rnd, unsigned long task_size,
- struct rlimit *rlim_stack)
-{
- unsigned long gap = rlim_stack->rlim_cur;
- unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;
- unsigned long gap_min, gap_max;
-
- /* Values close to RLIM_INFINITY can overflow. */
- if (gap + pad > gap)
- gap += pad;
-
- /*
- * Top of mmap area (just below the process stack).
- * Leave an at least ~128 MB hole with possible stack randomization.
- */
- gap_min = SIZE_128M;
- gap_max = (task_size / 6) * 5;
-
- if (gap < gap_min)
- gap = gap_min;
- else if (gap > gap_max)
- gap = gap_max;
-
- return PAGE_ALIGN(task_size - gap - rnd);
-}
-
-static unsigned long mmap_legacy_base(unsigned long rnd,
- unsigned long task_size)
-{
- return __TASK_UNMAPPED_BASE(task_size) + rnd;
-}
-
-/*
- * This function, called very early during the creation of a new
- * process VM image, sets up which VM layout function to use:
- */
-static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
- unsigned long random_factor, unsigned long task_size,
- struct rlimit *rlim_stack)
-{
- *legacy_base = mmap_legacy_base(random_factor, task_size);
- if (mmap_is_legacy())
- *base = *legacy_base;
- else
- *base = mmap_base(random_factor, task_size, rlim_stack);
-}
-
-void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
-{
- if (mmap_is_legacy())
- mm->get_unmapped_area = arch_get_unmapped_area;
- else
- mm->get_unmapped_area = arch_get_unmapped_area_topdown;
-
- arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base,
- arch_rnd(mmap64_rnd_bits), task_size_64bit(0),
- rlim_stack);
-
-#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
- /*
- * The mmap syscall mapping base decision depends solely on the
- * syscall type (64-bit or compat). This applies for 64bit
- * applications and 32bit applications. The 64bit syscall uses
- * mmap_base, the compat syscall uses mmap_compat_base.
- */
- arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base,
- arch_rnd(mmap32_rnd_bits), task_size_32bit(),
- rlim_stack);
-#endif
-}
-
unsigned long get_mmap_base(int is_legacy)
{
struct mm_struct *mm = current->mm;
diff --git a/mm/util.c b/mm/util.c
index ab3711c445e6..91a26da501d3 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -344,7 +344,7 @@ unsigned long randomize_stack_top(unsigned long stack_top)
}
#ifdef CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
-unsigned long arch_randomize_brk(struct mm_struct *mm)
+unsigned long __weak arch_randomize_brk(struct mm_struct *mm)
{
/* Is the current task 32bit ? */
if (!IS_ENABLED(CONFIG_64BIT) || is_compat_task())
--
2.30.2
