From 925f426451182a9f3e0f7f0e7e928f32f81a966a Mon Sep 17 00:00:00 2001 From: "Mike Rapoport (Microsoft)" Date: Sun, 26 Jan 2025 09:47:28 +0200 Subject: execmem: don't remove ROX cache from the direct map The memory allocated for the ROX cache was removed from the direct map to reduce amount of direct map updates, however this cannot be tolerated by /proc/kcore that accesses module memory using vread_iter() and the latter does vmalloc_to_page() and copy_page_to_iter_nofault(). Instead of removing ROX cache memory from the direct map and mapping it as ROX in vmalloc space, simply call set_memory_rox() that will take care of proper permissions on both vmalloc and in the direct map. Signed-off-by: "Mike Rapoport (Microsoft)" Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20250126074733.1384926-5-rppt@kernel.org --- mm/execmem.c | 17 ++++------------- 1 file changed, 4 insertions(+), 13 deletions(-) (limited to 'mm/execmem.c') diff --git a/mm/execmem.c b/mm/execmem.c index 317b6a8d35be..04b0bf1b5025 100644 --- a/mm/execmem.c +++ b/mm/execmem.c @@ -257,7 +257,6 @@ out_unlock: static int execmem_cache_populate(struct execmem_range *range, size_t size) { unsigned long vm_flags = VM_ALLOW_HUGE_VMAP; - unsigned long start, end; struct vm_struct *vm; size_t alloc_size; int err = -ENOMEM; @@ -275,26 +274,18 @@ static int execmem_cache_populate(struct execmem_range *range, size_t size) /* fill memory with instructions that will trap */ execmem_fill_trapping_insns(p, alloc_size, /* writable = */ true); - start = (unsigned long)p; - end = start + alloc_size; - - vunmap_range(start, end); - - err = execmem_set_direct_map_valid(vm, false); - if (err) - goto err_free_mem; - - err = vmap_pages_range_noflush(start, end, range->pgprot, vm->pages, - PMD_SHIFT); + err = set_memory_rox((unsigned long)p, vm->nr_pages); if (err) goto err_free_mem; err = execmem_cache_add(p, alloc_size); if (err) - goto err_free_mem; + goto err_reset_direct_map; return 0; +err_reset_direct_map: + execmem_set_direct_map_valid(vm, true); err_free_mem: vfree(p); return err; -- cgit v1.2.3 From 05e555b817262b5df6aa3a73df8b3dc9d388a3b4 Mon Sep 17 00:00:00 2001 From: "Mike Rapoport (Microsoft)" Date: Sun, 26 Jan 2025 09:47:29 +0200 Subject: execmem: add API for temporal remapping as RW and restoring ROX afterwards Using a writable copy for ROX memory is cumbersome and error prone. Add API that allow temporarily remapping of ranges in the ROX cache as writable and then restoring their read-only-execute permissions. This API will be later used in modules code and will allow removing nasty games with writable copy in alternatives patching on x86. The restoring of the ROX permissions relies on the ability of architecture to reconstruct large pages in its set_memory_rox() method. Signed-off-by: "Mike Rapoport (Microsoft)" Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20250126074733.1384926-6-rppt@kernel.org --- include/linux/execmem.h | 31 +++++++++++++++++++++++++++++++ mm/execmem.c | 22 ++++++++++++++++++++++ 2 files changed, 53 insertions(+) (limited to 'mm/execmem.c') diff --git a/include/linux/execmem.h b/include/linux/execmem.h index 64130ae19690..65655a5d1be2 100644 --- a/include/linux/execmem.h +++ b/include/linux/execmem.h @@ -65,6 +65,37 @@ enum execmem_range_flags { * Architectures that use EXECMEM_ROX_CACHE must implement this. */ void execmem_fill_trapping_insns(void *ptr, size_t size, bool writable); + +/** + * execmem_make_temp_rw - temporarily remap region with read-write + * permissions + * @ptr: address of the region to remap + * @size: size of the region to remap + * + * Remaps a part of the cached large page in the ROX cache in the range + * [@ptr, @ptr + @size) as writable and not executable. The caller must + * have exclusive ownership of this range and ensure nothing will try to + * execute code in this range. + * + * Return: 0 on success or negative error code on failure. + */ +int execmem_make_temp_rw(void *ptr, size_t size); + +/** + * execmem_restore_rox - restore read-only-execute permissions + * @ptr: address of the region to remap + * @size: size of the region to remap + * + * Restores read-only-execute permissions on a range [@ptr, @ptr + @size) + * after it was temporarily remapped as writable. Relies on architecture + * implementation of set_memory_rox() to restore mapping using large pages. + * + * Return: 0 on success or negative error code on failure. + */ +int execmem_restore_rox(void *ptr, size_t size); +#else +static inline int execmem_make_temp_rw(void *ptr, size_t size) { return 0; } +static inline int execmem_restore_rox(void *ptr, size_t size) { return 0; } #endif /** diff --git a/mm/execmem.c b/mm/execmem.c index 04b0bf1b5025..e6c4f5076ca8 100644 --- a/mm/execmem.c +++ b/mm/execmem.c @@ -335,6 +335,28 @@ static bool execmem_cache_free(void *ptr) return true; } + +int execmem_make_temp_rw(void *ptr, size_t size) +{ + unsigned int nr = PAGE_ALIGN(size) >> PAGE_SHIFT; + unsigned long addr = (unsigned long)ptr; + int ret; + + ret = set_memory_nx(addr, nr); + if (ret) + return ret; + + return set_memory_rw(addr, nr); +} + +int execmem_restore_rox(void *ptr, size_t size) +{ + unsigned int nr = PAGE_ALIGN(size) >> PAGE_SHIFT; + unsigned long addr = (unsigned long)ptr; + + return set_memory_rox(addr, nr); +} + #else /* CONFIG_ARCH_HAS_EXECMEM_ROX */ static void *execmem_cache_alloc(struct execmem_range *range, size_t size) { -- cgit v1.2.3