[PATCH v2 2/5] um: Limit TASK_SIZE to the addressable range

[benjamin]

From: Benjamin Berg <benjamin.b...@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.b...@intel.com>
---
 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 0d8b1a73cd5b..5ab1a92b6bf7 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -337,11 +337,16 @@ 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 > 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();
-- 
2.45.1