um: Catch unprotected user memory access
If the kernel tries to access user memory without copy_from_user()
a trap will happen as kernel and userspace run in different processes
on the host side. Currently this special page fault cannot be resolved
and will happen over and over again. As result UML will lockup.
This patch allows the page fault code to detect that situation and
causes a panic() such that the root cause of the unprotected memory
access can be found and fixed.
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 8e4daf4..34b633ec 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -219,6 +219,11 @@
show_regs(container_of(regs, struct pt_regs, regs));
panic("Segfault with no mm");
}
+ else if (!is_user && address < TASK_SIZE) {
+ show_regs(container_of(regs, struct pt_regs, regs));
+ panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
+ address, ip);
+ }
if (SEGV_IS_FIXABLE(&fi))
err = handle_page_fault(address, ip, is_write, is_user,
