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

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Message-ID: <Y10OyLCLAAS6rsZv@hirez.programming.kicks-ass.net>
Date:   Sat, 29 Oct 2022 13:30:16 +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 Thu, Oct 27, 2022 at 08:59:45AM +0200, Peter Zijlstra wrote:
> On Wed, Oct 26, 2022 at 10:59:29AM -0700, Linus Torvalds wrote:
> 
> > Maybe you meant to do that, and this patch was just prep-work for the
> > arch code being the second stage?
> 
> Yeah; also, since this is cross arch, we need a fallback. Anyway;
> robots hated on me for missing a few includes. I'll go prod at this
> more.

Got around to it; I added the below patch on top and things seem to
still boot so it must be good :-)

---
Subject: x86/mm: Implement native set_memory_rox()
From: Peter Zijlstra <peterz@...radead.org>
Date: Sat Oct 29 13:19:31 CEST 2022

Provide a native implementation of set_memory_rox(), avoiding the
double set_memory_ro();set_memory_x(); calls.

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/set_memory.h |    3 +++
 arch/x86/mm/pat/set_memory.c      |   10 ++++++++++
 include/linux/set_memory.h        |    2 ++
 3 files changed, 15 insertions(+)

--- a/arch/x86/include/asm/set_memory.h
+++ b/arch/x86/include/asm/set_memory.h
@@ -6,6 +6,9 @@
 #include <asm/page.h>
 #include <asm-generic/set_memory.h>
 
+#define set_memory_rox set_memory_rox
+int set_memory_rox(unsigned long addr, int numpages);
+
 /*
  * The set_memory_* API can be used to change various attributes of a virtual
  * address range. The attributes include:
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2025,6 +2025,16 @@ int set_memory_ro(unsigned long addr, in
 	return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_RW), 0);
 }
 
+int set_memory_rox(unsigned long addr, int numpages)
+{
+	pgprot_t clr = __pgprot(_PAGE_RW);
+
+	if (__supported_pte_mask & _PAGE_NX)
+		clr.pgprot |= _PAGE_NX;
+
+	return change_page_attr_clear(&addr, numpages, clr, 0);
+}
+
 int set_memory_rw(unsigned long addr, int numpages)
 {
 	return change_page_attr_set(&addr, numpages, __pgprot(_PAGE_RW), 0);
--- a/include/linux/set_memory.h
+++ b/include/linux/set_memory.h
@@ -14,6 +14,7 @@ static inline int set_memory_x(unsigned
 static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
 #endif
 
+#ifndef set_memory_rox
 static inline int set_memory_rox(unsigned long addr, int numpages)
 {
 	int ret = set_memory_ro(addr, numpages);
@@ -21,6 +22,7 @@ static inline int set_memory_rox(unsigne
 		return ret;
 	return set_memory_x(addr, numpages);
 }
+#endif
 
 #ifndef CONFIG_ARCH_HAS_SET_DIRECT_MAP
 static inline int set_direct_map_invalid_noflush(struct page *page)