The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x a82b26451de126a5ae130361081986bc459afe9b # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025062013-chlorine-rubbing-22b0@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a82b26451de126a5ae130361081986bc459afe9b Mon Sep 17 00:00:00 2001 From: "Peter Zijlstra (Intel)" peterz@infradead.org Date: Tue, 3 Jun 2025 14:14:44 +0300 Subject: [PATCH] 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

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index b50fe6ce4655..6455f7f751b3 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; + execmem_make_temp_rw(page, PAGE_SIZE); + if (pages == &its_pages) + set_memory_x((unsigned long)page, 1);

- pages->pages = tmp; - pages->pages[pages->num++] = page; - - 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.