Re: [PATCH 0/5] x86/ftrace: Cure boot time W+X mapping

[Peter Zijlstra]

On Tue, Oct 25, 2022 at 04:07:25PM -0700, Linus Torvalds wrote:

> It does strike me that it's stupid to make those be two calls that do
> exactly the same thing, and we should have a combined "set it
> read-only and executable" function, but that's a separate issue.

Right, and we have it all over the place. Something like the below
perhaps? I'll feed it to the robots, see if something breaks.

> The slowness is probably not the trampilines, but just the regular
> "text_poke of kernel text" that we probably want to keep special just
> because otherwise it's _so_ slow to do for every alternative etc.

I tried with and without the patches, it's dead slow either way and I
couldn't spot a noticable difference between the two -- so I'm assuming
it's simply the trace overhead, not the trace-enable time.


---
--- a/arch/arm/mach-omap1/sram-init.c
+++ b/arch/arm/mach-omap1/sram-init.c
@@ -74,8 +74,7 @@ void *omap_sram_push(void *funcp, unsign
 
 	dst = fncpy(sram, funcp, size);
 
-	set_memory_ro(base, pages);
-	set_memory_x(base, pages);
+	set_memory_rox(base, pages);
 
 	return dst;
 }
@@ -126,8 +125,7 @@ static void __init omap_detect_and_map_s
 	base = (unsigned long)omap_sram_base;
 	pages = PAGE_ALIGN(omap_sram_size) / PAGE_SIZE;
 
-	set_memory_ro(base, pages);
-	set_memory_x(base, pages);
+	set_memory_rox(base, pages);
 }
 
 static void (*_omap_sram_reprogram_clock)(u32 dpllctl, u32 ckctl);
--- a/arch/arm/mach-omap2/sram.c
+++ b/arch/arm/mach-omap2/sram.c
@@ -96,8 +96,7 @@ void *omap_sram_push(void *funcp, unsign
 
 	dst = fncpy(sram, funcp, size);
 
-	set_memory_ro(base, pages);
-	set_memory_x(base, pages);
+	set_memory_rox(base, pages);
 
 	return dst;
 }
@@ -217,8 +216,7 @@ static void __init omap2_map_sram(void)
 	base = (unsigned long)omap_sram_base;
 	pages = PAGE_ALIGN(omap_sram_size) / PAGE_SIZE;
 
-	set_memory_ro(base, pages);
-	set_memory_x(base, pages);
+	set_memory_rox(base, pages);
 }
 
 static void (*_omap2_sram_ddr_init)(u32 *slow_dll_ctrl, u32 fast_dll_ctrl,
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -134,10 +134,9 @@ void *alloc_insn_page(void)
 	if (!page)
 		return NULL;
 
-	if (strict_module_rwx_enabled()) {
-		set_memory_ro((unsigned long)page, 1);
-		set_memory_x((unsigned long)page, 1);
-	}
+	if (strict_module_rwx_enabled())
+		set_memory_rox((unsigned long)page, 1);
+
 	return page;
 }
 
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -415,8 +415,7 @@ create_trampoline(struct ftrace_ops *ops
 
 	set_vm_flush_reset_perms(trampoline);
 
-	set_memory_ro((unsigned long)trampoline, npages);
-	set_memory_x((unsigned long)trampoline, npages);
+	set_memory_rox((unsigned long)trampoline, npages);
 	return (unsigned long)trampoline;
 fail:
 	tramp_free(trampoline);
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -415,17 +415,12 @@ void *alloc_insn_page(void)
 		return NULL;
 
 	set_vm_flush_reset_perms(page);
-	/*
-	 * First make the page read-only, and only then make it executable to
-	 * prevent it from being W+X in between.
-	 */
-	set_memory_ro((unsigned long)page, 1);
 
 	/*
 	 * TODO: Once additional kernel code protection mechanisms are set, ensure
 	 * that the page was not maliciously altered and it is still zeroed.
 	 */
-	set_memory_x((unsigned long)page, 1);
+	set_memory_rox((unsigned long)page, 1);
 
 	return page;
 }
--- a/drivers/misc/sram-exec.c
+++ b/drivers/misc/sram-exec.c
@@ -106,10 +106,7 @@ void *sram_exec_copy(struct gen_pool *po
 
 	dst_cpy = fncpy(dst, src, size);
 
-	ret = set_memory_ro((unsigned long)base, pages);
-	if (ret)
-		goto error_out;
-	ret = set_memory_x((unsigned long)base, pages);
+	ret = set_memory_rox((unsigned long)base, pages);
 	if (ret)
 		goto error_out;
 
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -860,8 +860,7 @@ static inline void bpf_prog_lock_ro(stru
 static inline void bpf_jit_binary_lock_ro(struct bpf_binary_header *hdr)
 {
 	set_vm_flush_reset_perms(hdr);
-	set_memory_ro((unsigned long)hdr, hdr->size >> PAGE_SHIFT);
-	set_memory_x((unsigned long)hdr, hdr->size >> PAGE_SHIFT);
+	set_memory_rox((unsigned long)hdr, hdr->size >> PAGE_SHIFT);
 }
 
 int sk_filter_trim_cap(struct sock *sk, struct sk_buff *skb, unsigned int cap);
--- a/include/linux/set_memory.h
+++ b/include/linux/set_memory.h
@@ -14,6 +14,14 @@ static inline int set_memory_x(unsigned
 static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
 #endif
 
+static inline int set_memory_rox(unsigned long addr, int numpages)
+{
+	int ret = set_memory_ro(addr, numpages);
+	if (ret)
+		return ret;
+	return set_memory_x(addr, numpages);
+}
+
 #ifndef CONFIG_ARCH_HAS_SET_DIRECT_MAP
 static inline int set_direct_map_invalid_noflush(struct page *page)
 {
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -494,8 +494,7 @@ static int bpf_struct_ops_map_update_ele
 	refcount_set(&kvalue->refcnt, 1);
 	bpf_map_inc(map);
 
-	set_memory_ro((long)st_map->image, 1);
-	set_memory_x((long)st_map->image, 1);
+	set_memory_rox((long)st_map->image, 1);
 	err = st_ops->reg(kdata);
 	if (likely(!err)) {
 		/* Pair with smp_load_acquire() during lookup_elem().
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -864,8 +864,7 @@ static struct bpf_prog_pack *alloc_new_p
 	list_add_tail(&pack->list, &pack_list);
 
 	set_vm_flush_reset_perms(pack->ptr);
-	set_memory_ro((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
-	set_memory_x((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
+	set_memory_rox((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
 	return pack;
 }
 
@@ -883,8 +882,7 @@ void *bpf_prog_pack_alloc(u32 size, bpf_
 		if (ptr) {
 			bpf_fill_ill_insns(ptr, size);
 			set_vm_flush_reset_perms(ptr);
-			set_memory_ro((unsigned long)ptr, size / PAGE_SIZE);
-			set_memory_x((unsigned long)ptr, size / PAGE_SIZE);
+			set_memory_rox((unsigned long)ptr, size / PAGE_SIZE);
 		}
 		goto out;
 	}
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -468,8 +468,7 @@ static int bpf_trampoline_update(struct
 	if (err < 0)
 		goto out;
 
-	set_memory_ro((long)im->image, 1);
-	set_memory_x((long)im->image, 1);
+	set_memory_rox((long)im->image, 1);
 
 	WARN_ON(tr->cur_image && tr->selector == 0);
 	WARN_ON(!tr->cur_image && tr->selector);
--- a/net/bpf/bpf_dummy_struct_ops.c
+++ b/net/bpf/bpf_dummy_struct_ops.c
@@ -124,8 +124,7 @@ int bpf_struct_ops_test_run(struct bpf_p
 	if (err < 0)
 		goto out;
 
-	set_memory_ro((long)image, 1);
-	set_memory_x((long)image, 1);
+	set_memory_rox((long)image, 1);
 	prog_ret = dummy_ops_call_op(image, args);
 
 	err = dummy_ops_copy_args(args);