On Wed, May 28, 2025 at 02:35:57PM +0200, Juergen Gross wrote:
When allocating memory pages for kernel ITS thunks, make them read-only after having written the last thunk.
This will be needed when X86_FEATURE_PSE isn't available, as the thunk memory will have PAGE_KERNEL_EXEC protection, which is including the write permission.
Cc: stable@vger.kernel.org Fixes: 5185e7f9f3bd ("x86/module: enable ROX caches for module text on 64 bit") Signed-off-by: Juergen Gross jgross@suse.com
arch/x86/kernel/alternative.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index ecfe7b497cad..bd974a0ac88a 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -217,6 +217,15 @@ static void *its_alloc(void) return no_free_ptr(page); } +static void its_set_kernel_ro(void *addr) +{ +#ifdef CONFIG_MODULES
- if (its_mod)
return;+#endif
- execmem_restore_rox(addr, PAGE_SIZE);
+}
static void *its_allocate_thunk(int reg) { int size = 3 + (reg / 8); @@ -234,6 +243,8 @@ static void *its_allocate_thunk(int reg) #endif if (!its_page || (its_offset + size - 1) >= PAGE_SIZE) {
if (its_page)its_set_kernel_ro(its_page);@@ -2338,6 +2349,11 @@ void __init alternative_instructions(void) apply_retpolines(__retpoline_sites, __retpoline_sites_end); apply_returns(__return_sites, __return_sites_end);
- /* Make potential last thunk page read-only. */
- if (its_page)
its_set_kernel_ro(its_page);- its_page = NULL;
- /*
- Adjust all CALL instructions to point to func()-10, including
- those in .altinstr_replacement.
No, this is all sorts of wrong. Execmem API should ensure this.