um: Limit TASK_SIZE to the addressable range

We may have a TASK_SIZE from the host that is bigger than UML is able to
address with a three-level pagetable on 64-bit. Guard against that by
clipping the maximum TASK_SIZE to the maximum addressable area.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20240919124511.282088-8-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 427024f32b9fe35c0aec4efecf211db6994848f7..4452df4f2c4b48cafb371b911c917dd4f785a376 100644 (file)
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -331,11 +331,16 @@ 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();