[RFC PATCH v6 04/11] mm/mmap: Add IBT bitmap size to address space limit check

[Yu-cheng Yu]

The indirect branch tracking legacy bitmap takes a large address
space.  This causes may_expand_vm() failure on the address limit
check.  For a IBT-enabled task, add the bitmap size to the
address limit.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
 arch/x86/include/asm/mmu_context.h | 10 ++++++++++
 mm/mmap.c                          | 19 ++++++++++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 57c1f6c42bef..97a101267dd5 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -341,4 +341,14 @@ static inline unsigned long __get_current_cr3_fast(void)
 	return cr3;
 }
 
+#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
+static inline unsigned long arch_as_limit(void)
+{
+	if (current->thread.cet.ibt_enabled)
+		return current->thread.cet.ibt_bitmap_size;
+	else
+		return 0;
+}
+#endif
+
 #endif /* _ASM_X86_MMU_CONTEXT_H */
diff --git a/mm/mmap.c b/mm/mmap.c
index 9560d69fa08c..3de023f3e565 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3283,13 +3283,30 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	return NULL;
 }
 
+#ifndef CONFIG_ARCH_HAS_AS_LIMIT
+static inline unsigned long arch_as_limit(void)
+{
+	return 0;
+}
+#endif
+
 /*
  * Return true if the calling process may expand its vm space by the passed
  * number of pages
  */
 bool may_expand_vm(struct mm_struct *mm, vm_flags_t flags, unsigned long npages)
 {
-	if (mm->total_vm + npages > rlimit(RLIMIT_AS) >> PAGE_SHIFT)
+	unsigned long as_limit = rlimit(RLIMIT_AS);
+	unsigned long as_limit_plus = as_limit + arch_as_limit();
+
+	/* as_limit_plus overflowed */
+	if (as_limit_plus < as_limit)
+		as_limit_plus = RLIM_INFINITY;
+
+	if (as_limit_plus > as_limit)
+		as_limit = as_limit_plus;
+
+	if (mm->total_vm + npages > as_limit >> PAGE_SHIFT)
 		return false;
 
 	if (is_data_mapping(flags) &&
-- 
2.17.1