[PATCH 08/16] x86: mm: Support MAP_BELOW_HINT
From: Charlie Jenkins <hidden>
Date: 2024-08-28 05:49:54
Also in:
linux-arch, linux-kselftest, linux-mips, linux-mm, linux-riscv, linux-s390, linux-sh, lkml, loongarch, sparclinux
Subsystem:
the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
Add support for MAP_BELOW_HINT to mmap by restricting high_limit to addr when the flag is enabled. Signed-off-by: Charlie Jenkins <redacted> --- arch/x86/kernel/sys_x86_64.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 01d7cd85ef97..fa16b38f3702 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c@@ -86,7 +86,7 @@ SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len, return ksys_mmap_pgoff(addr, len, prot, flags, fd, off >> PAGE_SHIFT); } -static void find_start_end(unsigned long addr, unsigned long flags, +static void find_start_end(unsigned long addr, unsigned long len, unsigned long flags, unsigned long *begin, unsigned long *end) { if (!in_32bit_syscall() && (flags & MAP_32BIT)) {
@@ -106,10 +106,14 @@ static void find_start_end(unsigned long addr, unsigned long flags, } *begin = get_mmap_base(1); + if (in_32bit_syscall()) *end = task_size_32bit(); else *end = task_size_64bit(addr > DEFAULT_MAP_WINDOW); + + if (flags & MAP_BELOW_HINT) + *end = MIN(*end, addr + len); } static inline unsigned long stack_guard_placement(vm_flags_t vm_flags)
@@ -132,7 +136,7 @@ arch_get_unmapped_area_vmflags(struct file *filp, unsigned long addr, unsigned l if (flags & MAP_FIXED) return addr; - find_start_end(addr, flags, &begin, &end); + find_start_end(addr, len, flags, &begin, &end); if (len > end) return -ENOMEM;
@@ -166,6 +170,7 @@ arch_get_unmapped_area_topdown_vmflags(struct file *filp, unsigned long addr0, struct mm_struct *mm = current->mm; unsigned long addr = addr0; struct vm_unmapped_area_info info = {}; + unsigned long task_size, mmap_base; /* requested length too big for entire address space */ if (len > TASK_SIZE)
@@ -198,7 +203,8 @@ arch_get_unmapped_area_topdown_vmflags(struct file *filp, unsigned long addr0, else info.low_limit = PAGE_SIZE; - info.high_limit = get_mmap_base(0); + mmap_base = get_mmap_base(0); + info.high_limit = mmap_base; info.start_gap = stack_guard_placement(vm_flags); /*
@@ -210,6 +216,19 @@ arch_get_unmapped_area_topdown_vmflags(struct file *filp, unsigned long addr0, */ if (addr > DEFAULT_MAP_WINDOW && !in_32bit_syscall()) info.high_limit += TASK_SIZE_MAX - DEFAULT_MAP_WINDOW; + if (flags & MAP_BELOW_HINT) { +#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES + task_size = task_size_32bit(); +#else + task_size = task_size_64bit(0); +#endif + /* + * mmap_base is defined by PAGE_ALIGN(task_size - gap - rnd) so + * subtract out the task_size to isolate the gap + rnd. + */ + info.high_limit = MIN(info.high_limit, + (addr + len) - (task_size - mmap_base)); + } info.align_offset = pgoff << PAGE_SHIFT; if (filp) {
--
2.45.0