linux-kernel - [PATCH -v2] x86/ia32: State that IA32 emulation is disabled

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Message-ID: <20231206172022.GCZXCtVoZtt4t2TLpe@fat_crate.local>
Date:   Wed, 6 Dec 2023 18:20:22 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Nikolay Borisov <nik.borisov@...e.com>
Subject: [PATCH -v2] x86/ia32: State that IA32 emulation is disabled

From: "Borislav Petkov (AMD)" <bp@...en8.de>
Date: Thu, 30 Nov 2023 16:39:33 +0100

Issue a short message once, on the first try to load a 32-bit process to
save people time when wondering why it won't load and trying to execute
it, would say:

  -bash: ./strsep32: cannot execute binary file: Exec format error

Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Cc: Nikolay Borisov <nik.borisov@...e.com>
---
 arch/x86/include/asm/elf.h  |  2 +-
 arch/x86/include/asm/ia32.h | 11 ++++++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index a0234dfd1031..1e16bd5ac781 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -150,7 +150,7 @@ do {						\
 	((x)->e_machine == EM_X86_64)
 
 #define compat_elf_check_arch(x)					\
-	((elf_check_arch_ia32(x) && ia32_enabled()) ||			\
+	((elf_check_arch_ia32(x) && ia32_enabled_verbose()) ||		\
 	 (IS_ENABLED(CONFIG_X86_X32_ABI) && (x)->e_machine == EM_X86_64))
 
 static inline void elf_common_init(struct thread_struct *t,
diff --git a/arch/x86/include/asm/ia32.h b/arch/x86/include/asm/ia32.h
index 5a2ae24b1204..094886a8717e 100644
--- a/arch/x86/include/asm/ia32.h
+++ b/arch/x86/include/asm/ia32.h
@@ -2,7 +2,6 @@
 #ifndef _ASM_X86_IA32_H
 #define _ASM_X86_IA32_H
 
-
 #ifdef CONFIG_IA32_EMULATION
 
 #include <linux/compat.h>
@@ -84,4 +83,14 @@ static inline bool ia32_enabled(void)
 
 #endif
 
+static inline bool ia32_enabled_verbose(void)
+{
+	bool enabled = ia32_enabled();
+
+	if (IS_ENABLED(CONFIG_IA32_EMULATION) && !enabled)
+		pr_notice_once("32-bit emulation disabled. You can reenable with ia32_emulation=on\n");
+
+	return enabled;
+}
+
 #endif /* _ASM_X86_IA32_H */
-- 
2.42.0.rc0.25.ga82fb66fed25

-- 
Regards/Gruss,
    Boris.

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