[PATCH 1/5] um: Fix stub_start address calculation

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

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

The calculation was wrong as it only subtracted one and then rounded
down for alignment. However, this is incorrect if host_task_size is not
already aligned.

This probably worked fine because on 64 bit the host_task_size is bigger
than returned by os_get_top_address.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
---
arch/um/kernel/um_arch.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index e95f805e5004..0d8b1a73cd5b 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -331,7 +331,8 @@ int __init linux_main(int argc, char **argv)
/* reserve a few pages for the stubs (taking care of data alignment) */
/* align the data portion */
BUILD_BUG_ON(!is_power_of_2(STUB_DATA_PAGES));
- stub_start = (host_task_size - 1) & ~(STUB_DATA_PAGES * PAGE_SIZE - 1);
+ stub_start = (host_task_size - STUB_DATA_PAGES * PAGE_SIZE) &
+ ~(STUB_DATA_PAGES * PAGE_SIZE - 1);
/* another page for the code portion */
stub_start -= PAGE_SIZE;
host_task_size = stub_start;
--
2.45.1