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Subject[PATCHv2 3/5] x86/mm: fix native mmap() in compat bins and vice-versa
Date
Fix 32-bit compat_sys_mmap() mapping VMA over 4Gb in 64-bit binaries
and 64-bit sys_mmap() mapping VMA only under 4Gb in 32-bit binaries.
Changed arch_get_unmapped_area{,_topdown}() to recompute mmap_base
for those cases and use according high/low limits for vm_unmapped_area()
The recomputing of mmap_base may make compat sys_mmap() in 64-bit
binaries a little slower than native, which uses already known from exec
time mmap_base - but, as it returned buggy address, that case seemed
unused previously, so no performance degradation for already used ABI.
Can be optimized in future by introducing mmap_compat_{,legacy}_base
in mm_struct.

I discovered that bug on ZDTM tests for compat 32-bit C/R.
Working compat sys_mmap() in 64-bit binaries is really needed for that
purpose, as 32-bit applications are restored from 64-bit CRIU binary.

Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
---
arch/x86/kernel/sys_x86_64.c | 44 +++++++++++++++++++++++++++++++++++++++++---
1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index a55ed63b9f91..1bf90cd1400c 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -113,10 +113,31 @@ static void find_start_end(unsigned long flags, unsigned long *begin,
if (current->flags & PF_RANDOMIZE) {
*begin = randomize_page(*begin, 0x02000000);
}
+ return;
+ }
+
+ if (!test_thread_flag(TIF_ADDR32)) {
+#ifdef CONFIG_COMPAT
+ /* 64-bit native binary doing compat 32-bit syscall */
+ if (in_compat_syscall()) {
+ *begin = mmap_legacy_base(arch_compat_rnd(),
+ IA32_PAGE_OFFSET);
+ *end = IA32_PAGE_OFFSET;
+ return;
+ }
+#endif
} else {
- *begin = current->mm->mmap_legacy_base;
- *end = TASK_SIZE;
+ /* 32-bit binary doing 64-bit syscall */
+ if (!in_compat_syscall()) {
+ *begin = mmap_legacy_base(arch_native_rnd(),
+ IA32_PAGE_OFFSET);
+ *end = TASK_SIZE_MAX;
+ return;
+ }
}
+
+ *begin = current->mm->mmap_legacy_base;
+ *end = TASK_SIZE;
}

unsigned long
@@ -157,6 +178,23 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
return vm_unmapped_area(&info);
}

+static unsigned long find_top(void)
+{
+ if (!test_thread_flag(TIF_ADDR32)) {
+#ifdef CONFIG_COMPAT
+ /* 64-bit native binary doing compat 32-bit syscall */
+ if (in_compat_syscall())
+ return mmap_base(arch_compat_rnd(), IA32_PAGE_OFFSET);
+#endif
+ } else {
+ /* 32-bit binary doing 64-bit syscall */
+ if (!in_compat_syscall())
+ return mmap_base(arch_native_rnd(), TASK_SIZE_MAX);
+ }
+
+ return current->mm->mmap_base;
+}
+
unsigned long
arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
const unsigned long len, const unsigned long pgoff,
@@ -190,7 +228,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
info.flags = VM_UNMAPPED_AREA_TOPDOWN;
info.length = len;
info.low_limit = PAGE_SIZE;
- info.high_limit = mm->mmap_base;
+ info.high_limit = find_top();
info.align_mask = 0;
info.align_offset = pgoff << PAGE_SHIFT;
if (filp) {
--
2.11.0
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