[PATCH 2/2] um: Ensure that nobody remaps the stub vma

[Richard Weinberger]

This fixes a long standing problem that UML crashes
or locks up if a task messes with it' stub vma.

Reported-by: toralf.foerster@xxxxxx
Signed-off-by: Richard Weinberger <richard@xxxxxx>
---
 arch/um/kernel/tlb.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c
index 9472079..b33d1d1 100644
--- a/arch/um/kernel/tlb.c
+++ b/arch/um/kernel/tlb.c
@@ -12,6 +12,7 @@
 #include <mem_user.h>
 #include <os.h>
 #include <skas.h>
+#include <kern_util.h>
 
 struct host_vm_change {
 	struct host_vm_op {
@@ -90,6 +91,9 @@ static int add_mmap(unsigned long virt, unsigned long phys, unsigned long len,
 	struct host_vm_op *last;
 	int fd, ret = 0;
 
+	if ((virt >= STUB_START) && (virt < STUB_END))
+		return -EINVAL;
+
 	fd = phys_mapping(phys, &offset);
 	if (hvc->index != 0) {
 		last = &hvc->ops[hvc->index - 1];
@@ -124,6 +128,9 @@ static int add_munmap(unsigned long addr, unsigned long len,
 	struct host_vm_op *last;
 	int ret = 0;
 
+	if ((addr >= STUB_START) && (addr < STUB_END))
+		return -EINVAL;
+
 	if (hvc->index != 0) {
 		last = &hvc->ops[hvc->index - 1];
 		if ((last->type == MUNMAP) &&
@@ -283,8 +290,10 @@ void fix_range_common(struct mm_struct *mm, unsigned long start_addr,
 	/* This is not an else because ret is modified above */
 	if (ret) {
 		printk(KERN_ERR "fix_range_common: failed, killing current "
-		       "process\n");
-		force_sig(SIGKILL, current);
+		       "process: %d\n", task_tgid_vnr(current));
+		/* We are under mmap_sem, release it such that current can terminate */
+		up_write(&current->mm->mmap_sem);
+		fatal_sigsegv();
 	}
 }
 
@@ -409,6 +418,9 @@ void flush_tlb_page(struct vm_area_struct *vma, unsigned long address)
 		w = 0;
 	}
 
+	if ((address >= STUB_START) && (address < STUB_END))
+		goto kill;
+
 	mm_id = &mm->context.id;
 	prot = ((r ? UM_PROT_READ : 0) | (w ? UM_PROT_WRITE : 0) |
 		(x ? UM_PROT_EXEC : 0));
@@ -435,7 +447,7 @@ void flush_tlb_page(struct vm_area_struct *vma, unsigned long address)
 
 kill:
 	printk(KERN_ERR "Failed to flush page for address 0x%lx\n", address);
-	force_sig(SIGKILL, current);
+	fatal_sigsegv();
 }
 
 pgd_t *pgd_offset_proc(struct mm_struct *mm, unsigned long address)
-- 
1.8.1.4

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