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Message-ID: <Y1jek64pXOsougmz@hirez.programming.kicks-ass.net>
Date: Wed, 26 Oct 2022 09:15:31 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: rostedt@...dmis.org, dave.hansen@...el.com,
linux-kernel@...r.kernel.org, x86@...nel.org,
keescook@...omium.org, seanjc@...gle.com
Subject: Re: [PATCH 0/5] x86/ftrace: Cure boot time W+X mapping
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);
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