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

benjamin
2024-05-28T08:54:40Z

From: Benjamin Berg <benjamin.berg@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@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