Since the kernel allocated those tables on-demand without userspace
knowledge, it is also responsible for freeing them when the associated
mappings go away.
Here, the solution for this issue is to hook do_munmap() to check
whether one process is MPX enabled. If yes, those bounds tables covered
in the virtual address region which is being unmapped will be freed also.
Signed-off-by: Qiaowei Ren <qiaowei.ren@xxxxxxxxx>
---
arch/x86/include/asm/mmu_context.h | 16 +++
arch/x86/include/asm/mpx.h | 9 ++
arch/x86/mm/mpx.c | 181 ++++++++++++++++++++++++++++++++++++
include/asm-generic/mmu_context.h | 6 +
mm/mmap.c | 2 +
5 files changed, 214 insertions(+), 0 deletions(-)
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index be12c53..af70d4f 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -6,6 +6,7 @@
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/paravirt.h>
+#include <asm/mpx.h>
#ifndef CONFIG_PARAVIRT
#include <asm-generic/mm_hooks.h>
@@ -96,4 +97,19 @@ do { \
} while (0)
#endif
+static inline void arch_unmap(struct mm_struct *mm,
+ struct vm_area_struct *vma,
+ unsigned long start, unsigned long end)
+{
+#ifdef CONFIG_X86_INTEL_MPX
+ /*
+ * Check whether this vma comes from MPX-enabled application.
+ * If so, release this vma related bound tables.
+ */
+ if (mm->bd_addr && !(vma->vm_flags & VM_MPX))
+ mpx_unmap(mm, start, end);
+
+#endif
+}
+
#endif /* _ASM_X86_MMU_CONTEXT_H */
diff --git a/arch/x86/include/asm/mpx.h b/arch/x86/include/asm/mpx.h
index 6cb0853..e848a74 100644
--- a/arch/x86/include/asm/mpx.h
+++ b/arch/x86/include/asm/mpx.h
@@ -42,6 +42,13 @@
#define MPX_BD_SIZE_BYTES (1UL<<(MPX_BD_ENTRY_OFFSET+MPX_BD_ENTRY_SHIFT))
#define MPX_BT_SIZE_BYTES (1UL<<(MPX_BT_ENTRY_OFFSET+MPX_BT_ENTRY_SHIFT))
+#define MPX_BD_ENTRY_MASK ((1<<MPX_BD_ENTRY_OFFSET)-1)
+#define MPX_BT_ENTRY_MASK ((1<<MPX_BT_ENTRY_OFFSET)-1)
+#define MPX_GET_BD_ENTRY_OFFSET(addr) ((((addr)>>(MPX_BT_ENTRY_OFFSET+ \
+ MPX_IGN_BITS)) & MPX_BD_ENTRY_MASK) << MPX_BD_ENTRY_SHIFT)
+#define MPX_GET_BT_ENTRY_OFFSET(addr) ((((addr)>>MPX_IGN_BITS) & \
+ MPX_BT_ENTRY_MASK) << MPX_BT_ENTRY_SHIFT)
+
#define MPX_BNDSTA_ERROR_CODE 0x3
#define MPX_BNDCFG_ENABLE_FLAG 0x1
#define MPX_BD_ENTRY_VALID_FLAG 0x1
@@ -63,6 +70,8 @@ struct mpx_insn {
#define MAX_MPX_INSN_SIZE 15
unsigned long mpx_mmap(unsigned long len);
+void mpx_unmap(struct mm_struct *mm,
+ unsigned long start, unsigned long end);
#ifdef CONFIG_X86_INTEL_MPX
int do_mpx_bt_fault(struct xsave_struct *xsave_buf);
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index e1b28e6..d29ec9c 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -2,6 +2,7 @@
#include <linux/syscalls.h>
#include <asm/mpx.h>
#include <asm/mman.h>
+#include <asm/mmu_context.h>
#include <linux/sched/sysctl.h>
static const char *mpx_mapping_name(struct vm_area_struct *vma)
@@ -77,3 +78,183 @@ out:
up_write(&mm->mmap_sem);
return ret;
}
+
+/*
+ * Get the base of bounds tables pointed by specific bounds
+ * directory entry.
+ */
+static int get_bt_addr(long __user *bd_entry, unsigned long *bt_addr,
+ unsigned int *valid)
+{
+ if (get_user(*bt_addr, bd_entry))
+ return -EFAULT;
+
+ *valid = *bt_addr & MPX_BD_ENTRY_VALID_FLAG;
+ *bt_addr &= MPX_BT_ADDR_MASK;
+
+ /*
+ * If this bounds directory entry is nonzero, and meanwhile
+ * the valid bit is zero, one SIGSEGV will be produced due to
+ * this unexpected situation.
+ */
+ if (!(*valid) && *bt_addr)
+ force_sig(SIGSEGV, current);
+
+ return 0;
+}
+
+/*
+ * Free the backing physical pages of bounds table 'bt_addr'.
+ * Assume start...end is within that bounds table.
+ */
+static void zap_bt_entries(struct mm_struct *mm, unsigned long bt_addr,
+ unsigned long start, unsigned long end)
+{
+ struct vm_area_struct *vma;
+
+ /* Find the vma which overlaps this bounds table */
+ vma = find_vma(mm, bt_addr);
+ if (!vma || vma->vm_start > bt_addr ||
+ vma->vm_end < bt_addr+MPX_BT_SIZE_BYTES)
+ return;
+
+ zap_page_range(vma, start, end, NULL);
+}
+
+static void unmap_single_bt(struct mm_struct *mm, long __user *bd_entry,
+ unsigned long bt_addr)
+{
+ if (user_atomic_cmpxchg_inatomic(&bt_addr, bd_entry,
+ bt_addr | MPX_BD_ENTRY_VALID_FLAG, 0))
+ return;
+
+ /*
+ * to avoid recursion, do_munmap() will check whether it comes
+ * from one bounds table through VM_MPX flag.
+ */
+ do_munmap(mm, bt_addr & MPX_BT_ADDR_MASK, MPX_BT_SIZE_BYTES);
+}
+
+/*
+ * If the bounds table pointed by bounds directory 'bd_entry' is
+ * not shared, unmap this whole bounds table. Otherwise, only free
+ * those backing physical pages of bounds table entries covered
+ * in this virtual address region start...end.
+ */
+static void unmap_shared_bt(struct mm_struct *mm, long __user *bd_entry,
+ unsigned long start, unsigned long end,
+ bool prev_shared, bool next_shared)
+{
+ unsigned long bt_addr;
+ unsigned int bde_valid = 0;
+
+ if (get_bt_addr(bd_entry, &bt_addr, &bde_valid) || !bde_valid)
+ return;
+
+ if (prev_shared && next_shared)
+ zap_bt_entries(mm, bt_addr,
+ bt_addr+MPX_GET_BT_ENTRY_OFFSET(start),
+ bt_addr+MPX_GET_BT_ENTRY_OFFSET(end-1));
+ else if (prev_shared)
+ zap_bt_entries(mm, bt_addr,
+ bt_addr+MPX_GET_BT_ENTRY_OFFSET(start),
+ bt_addr+MPX_BT_SIZE_BYTES);
+ else if (next_shared)
+ zap_bt_entries(mm, bt_addr, bt_addr,
+ bt_addr+MPX_GET_BT_ENTRY_OFFSET(end-1));
+ else
+ unmap_single_bt(mm, bd_entry, bt_addr);
+}
+
+/*
+ * A virtual address region being munmap()ed might share bounds table
+ * with adjacent VMAs. We only need to free the backing physical
+ * memory of these shared bounds tables entries covered in this virtual
+ * address region.
+ *
+ * the VMAs covering the virtual address region start...end have already
+ * been split if necessary and removed from the VMA list.
+ */
+static void unmap_side_bts(struct mm_struct *mm, unsigned long start,
+ unsigned long end)
+{
+ long __user *bde_start, *bde_end;
+ struct vm_area_struct *prev, *next;
+ bool prev_shared = false, next_shared = false;
+
+ bde_start = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(start);
+ bde_end = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(end-1);
+
+ /*
+ * Check whether bde_start and bde_end are shared with adjacent
+ * VMAs. Because the VMAs covering the virtual address region
+ * start...end have already been removed from the VMA list, if
+ * next is not NULL it will satisfy start < end <= next->vm_start.
+ * And if prev is not NULL, prev->vm_end <= start < end.
+ */
+ next = find_vma_prev(mm, start, &prev);
+ if (prev && MPX_GET_BD_ENTRY_OFFSET(prev->vm_end-1) == (long)bde_start)
+ prev_shared = true;
+ if (next && MPX_GET_BD_ENTRY_OFFSET(next->vm_start) == (long)bde_end)
+ next_shared = true;
+
+ /*
+ * This virtual address region being munmap()ed is only
+ * covered by one bounds table.
+ *
+ * In this case, if this table is also shared with adjacent
+ * VMAs, only part of the backing physical memory of the bounds
+ * table need be freeed. Otherwise the whole bounds table need
+ * be unmapped.
+ */
+ if (bde_start == bde_end) {
+ unmap_shared_bt(mm, bde_start, start, end,
+ prev_shared, next_shared);
+ return;
+ }
+
+ /*
+ * If more than one bounds tables are covered in this virtual
+ * address region being munmap()ed, we need to separately check
+ * whether bde_start and bde_end are shared with adjacent VMAs.
+ */
+ unmap_shared_bt(mm, bde_start, start, end, prev_shared, false);
+ unmap_shared_bt(mm, bde_end, start, end, false, next_shared);
+}
+
+/*
+ * Free unused bounds tables covered in a virtual address region being
+ * munmap()ed. Assume end > start.
+ *
+ * This function will be called by do_munmap(), and the VMAs covering
+ * the virtual address region start...end have already been split if
+ * necessary and remvoed from the VMA list.
+ */
+void mpx_unmap(struct mm_struct *mm,
+ unsigned long start, unsigned long end)
+{
+ long __user *bd_entry, *bde_start, *bde_end;
+ unsigned long bt_addr;
+ unsigned int bde_valid;
+
+ /*
+ * unmap bounds tables pointed out by start/end bounds directory
+ * entries, or only free part of their backing physical memroy
+ * if they are shared with adjacent VMAs.
+ */
+ unmap_side_bts(mm, start, end);
+
+ /*
+ * unmap those bounds table which are entirely covered in this
+ * virtual address region.
+ */
+ bde_start = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(start);
+ bde_end = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(end-1);
+ for (bd_entry = bde_start + 1; bd_entry < bde_end; bd_entry++) {
+ if (get_bt_addr(bd_entry, &bt_addr, &bde_valid))
+ return;
+ if (!bde_valid)
+ continue;
+ unmap_single_bt(mm, bd_entry, bt_addr);
+ }
+}
diff --git a/include/asm-generic/mmu_context.h b/include/asm-generic/mmu_context.h
index a7eec91..ac558ca 100644
--- a/include/asm-generic/mmu_context.h
+++ b/include/asm-generic/mmu_context.h
@@ -42,4 +42,10 @@ static inline void activate_mm(struct mm_struct *prev_mm,
{
}
+static inline void arch_unmap(struct mm_struct *mm,
+ struct vm_area_struct *vma,
+ unsigned long start, unsigned long end)
+{
+}
+
#endif /* __ASM_GENERIC_MMU_CONTEXT_H */
diff --git a/mm/mmap.c b/mm/mmap.c
index 129b847..8550d84 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2560,6 +2560,8 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
/* Fix up all other VM information */
remove_vma_list(mm, vma);
+ arch_unmap(mm, vma, start, end);
+
return 0;
}
--
1.7.1
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