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authorBenjamin Berg <benjamin.berg@intel.com>2024-09-19 14:45:07 +0200
committerJohannes Berg <johannes.berg@intel.com>2024-10-10 13:37:22 +0200
commit91f0a0c5cc5bc863888a936fbd05394c6e284466 (patch)
tree6b42aa2932bf01d303eae08fafc4ce785c74f791 /arch/um
parent77eb31b6003a158cce534fa9ca9df21fc82672ea (diff)
um: Calculate stub data address relative to stub code
Instead of using the current stack pointer, we can also use the current instruction to calculate where the stub data is. With this the stub data only needs to be aligned to a full page boundary. Changing this has the advantage that we do not have a hole in the memory space above the stub data (which would need to be explicitly cleared). Another motivation to do this is that with the planned addition of a SECCOMP based userspace the stack pointer may not be fully trustworthy. Signed-off-by: Benjamin Berg <benjamin.berg@intel.com> Link: https://patch.msgid.link/20240919124511.282088-7-benjamin@sipsolutions.net Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Diffstat (limited to 'arch/um')
-rw-r--r--arch/um/kernel/um_arch.c6
1 files changed, 2 insertions, 4 deletions
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 99cdf4b2d648..427024f32b9f 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -325,10 +325,8 @@ int __init linux_main(int argc, char **argv)
add_arg(DEFAULT_COMMAND_LINE_CONSOLE);
host_task_size = os_get_top_address();
- /* 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);
+ /* reserve a few pages for the stubs */
+ stub_start = host_task_size - STUB_DATA_PAGES * PAGE_SIZE;
/* another page for the code portion */
stub_start -= PAGE_SIZE;
host_task_size = stub_start;