[PATCH v8 4/7] um: Limit TASK_SIZE to the addressable range

[Benjamin Berg]

From: Benjamin Berg <benjamin.berg at intel.com>

We may have a TASK_SIZE from the host that is bigger than UML is able to
address with a three-level pagetable. Guard against that by clipping the
maximum TASK_SIZE to the maximum addressable area.

Signed-off-by: Benjamin Berg <benjamin.berg at intel.com>

---

v7: Fix integer overflow on 32 bit with 3-level page tables
---
 arch/um/kernel/um_arch.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 25cd2c6d7e95..f82dd4e854f3 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -334,11 +334,16 @@ int __init linux_main(int argc, char **argv)
 	stub_start -= PAGE_SIZE;
 	host_task_size = stub_start;
 
+	/* Limit TASK_SIZE to what is addressable by the page table */
+	task_size = host_task_size;
+	if (task_size > (unsigned long long) PTRS_PER_PGD * PGDIR_SIZE)
+		task_size = PTRS_PER_PGD * PGDIR_SIZE;
+
 	/*
 	 * TASK_SIZE needs to be PGDIR_SIZE aligned or else exit_mmap craps
 	 * out
 	 */
-	task_size = host_task_size & PGDIR_MASK;
+	task_size = task_size & PGDIR_MASK;
 
 	/* OS sanity checks that need to happen before the kernel runs */
 	os_early_checks();
-- 
2.45.2