The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: a82b26451de126a5ae130361081986bc459afe9b Gitweb: https://git.kernel.org/tip/a82b26451de126a5ae130361081986bc459afe9b Author: Peter Zijlstra (Intel) peterz@infradead.org AuthorDate: Tue, 03 Jun 2025 14:14:44 +03:00 Committer: Peter Zijlstra peterz@infradead.org CommitterDate: Wed, 11 Jun 2025 11:20:52 +02:00
x86/its: explicitly manage permissions for ITS pages
execmem_alloc() sets permissions differently depending on the kernel configuration, CPU support for PSE and whether a page is allocated before or after mark_rodata_ro().
Add tracking for pages allocated for ITS when patching the core kernel and make sure the permissions for ITS pages are explicitly managed for both kernel and module allocations.
Fixes: 872df34d7c51 ("x86/its: Use dynamic thunks for indirect branches") Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Co-developed-by: Mike Rapoport (Microsoft) rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) rppt@kernel.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Nikolay Borisov nik.borisov@suse.com Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20250603111446.2609381-5-rppt@kernel.org --- arch/x86/kernel/alternative.c | 74 +++++++++++++++++++++++----------- 1 file changed, 52 insertions(+), 22 deletions(-)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index b50fe6c..6455f7f 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -116,6 +116,24 @@ static struct module *its_mod; #endif static void *its_page; static unsigned int its_offset; +struct its_array its_pages; + +static void *__its_alloc(struct its_array *pages) +{ + void *page __free(execmem) = execmem_alloc(EXECMEM_MODULE_TEXT, PAGE_SIZE); + if (!page) + return NULL; + + void *tmp = krealloc(pages->pages, (pages->num+1) * sizeof(void *), + GFP_KERNEL); + if (!tmp) + return NULL; + + pages->pages = tmp; + pages->pages[pages->num++] = page; + + return no_free_ptr(page); +}
/* Initialize a thunk with the "jmp *reg; int3" instructions. */ static void *its_init_thunk(void *thunk, int reg) @@ -151,6 +169,21 @@ static void *its_init_thunk(void *thunk, int reg) return thunk + offset; }
+static void its_pages_protect(struct its_array *pages) +{ + for (int i = 0; i < pages->num; i++) { + void *page = pages->pages[i]; + execmem_restore_rox(page, PAGE_SIZE); + } +} + +static void its_fini_core(void) +{ + if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) + its_pages_protect(&its_pages); + kfree(its_pages.pages); +} + #ifdef CONFIG_MODULES void its_init_mod(struct module *mod) { @@ -173,10 +206,8 @@ void its_fini_mod(struct module *mod) its_page = NULL; mutex_unlock(&text_mutex);
- for (int i = 0; i < mod->arch.its_pages.num; i++) { - void *page = mod->arch.its_pages.pages[i]; - execmem_restore_rox(page, PAGE_SIZE); - } + if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX)) + its_pages_protect(&mod->arch.its_pages); }
void its_free_mod(struct module *mod) @@ -194,28 +225,23 @@ void its_free_mod(struct module *mod)
static void *its_alloc(void) { - void *page __free(execmem) = execmem_alloc(EXECMEM_MODULE_TEXT, PAGE_SIZE); + struct its_array *pages = &its_pages; + void *page;
+#ifdef CONFIG_MODULE + if (its_mod) + pages = &its_mod->arch.its_pages; +#endif + + page = __its_alloc(pages); if (!page) return NULL;
-#ifdef CONFIG_MODULES - if (its_mod) { - struct its_array *pages = &its_mod->arch.its_pages; - void *tmp = krealloc(pages->pages, - (pages->num+1) * sizeof(void *), - GFP_KERNEL); - if (!tmp) - return NULL; - - pages->pages = tmp; - pages->pages[pages->num++] = page; + execmem_make_temp_rw(page, PAGE_SIZE); + if (pages == &its_pages) + set_memory_x((unsigned long)page, 1);
- execmem_make_temp_rw(page, PAGE_SIZE); - } -#endif /* CONFIG_MODULES */ - - return no_free_ptr(page); + return page; }
static void *its_allocate_thunk(int reg) @@ -269,7 +295,9 @@ u8 *its_static_thunk(int reg) return thunk; }
-#endif +#else +static inline void its_fini_core(void) {} +#endif /* CONFIG_MITIGATION_ITS */
/* * Nomenclature for variable names to simplify and clarify this code and ease @@ -2339,6 +2367,8 @@ void __init alternative_instructions(void) apply_retpolines(__retpoline_sites, __retpoline_sites_end); apply_returns(__return_sites, __return_sites_end);
+ its_fini_core(); + /* * Adjust all CALL instructions to point to func()-10, including * those in .altinstr_replacement.