linux-kernel - Re: [PATCH v10 03/15] x86/alternatives: Disable LASS when patching kernel alternatives

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251021200328.GMaPfnEDibnBrhNTmQ@fat_crate.local>
Date: Tue, 21 Oct 2025 22:03:28 +0200
From: Borislav Petkov <bp@...en8.de>
To: Sohil Mehta <sohil.mehta@...el.com>
Cc: x86@...nel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Jonathan Corbet <corbet@....net>,
	"H . Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...nel.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ard Biesheuvel <ardb@...nel.org>,
	"Kirill A . Shutemov" <kas@...nel.org>, Xin Li <xin@...or.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	Sean Christopherson <seanjc@...gle.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Vegard Nossum <vegard.nossum@...cle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	David Laight <david.laight.linux@...il.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Kees Cook <kees@...nel.org>, Tony Luck <tony.luck@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org
Subject: Re: [PATCH v10 03/15] x86/alternatives: Disable LASS when patching
 kernel alternatives

On Mon, Oct 06, 2025 at 11:51:07PM -0700, Sohil Mehta wrote:
> +static __always_inline void lass_clac(void)
> +{
> +	alternative("", "clac", X86_FEATURE_LASS);
> +}
> +
> +static __always_inline void lass_stac(void)
> +{
> +	alternative("", "stac", X86_FEATURE_LASS);
> +}

So I probably missed the whole discussion on how we arrived at
lass_{stac,clac}() but just in case, those names sound silly.

IOW, I'd do this ontop:

diff --git a/arch/x86/include/asm/smap.h b/arch/x86/include/asm/smap.h
index 3ecb4b0de1f9..066d83a6b1ff 100644
--- a/arch/x86/include/asm/smap.h
+++ b/arch/x86/include/asm/smap.h
@@ -55,16 +55,8 @@ static __always_inline void stac(void)
  * Use lass_stac()/lass_clac() when accessing kernel mappings
  * (!_PAGE_USER) in the lower half of the address space.
  */
-
-static __always_inline void lass_clac(void)
-{
-	alternative("", "clac", X86_FEATURE_LASS);
-}
-
-static __always_inline void lass_stac(void)
-{
-	alternative("", "stac", X86_FEATURE_LASS);
-}
+#define lass_disable()		stac()
+#define lass_enable()		clac()
 
 static __always_inline unsigned long smap_save(void)
 {
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 6a96dbc60bf1..6cdf5c226c51 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -2487,18 +2487,18 @@ __ro_after_init unsigned long text_poke_mm_addr;
 
 static void text_poke_memcpy(void *dst, const void *src, size_t len)
 {
-	lass_stac();
+	lass_disable();
 	__inline_memcpy(dst, src, len);
-	lass_clac();
+	lass_enable();
 }
 
 static void text_poke_memset(void *dst, const void *src, size_t len)
 {
 	int c = *(const int *)src;
 
-	lass_stac();
+	lass_disable();
 	__inline_memset(dst, c, len);
-	lass_clac();
+	lass_enable();
 }
 
 typedef void text_poke_f(void *dst, const void *src, size_t len);

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette