linux-kernel - [PATCH 2/4] kexec: add CONFING_KEXEC_PURGATORY_SKIP

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Date:   Mon, 25 Jul 2022 16:38:54 +0800
From:   Albert Huang <huangjie.albert@...edance.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     "huangjie.albert" <huangjie.albert@...edance.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Michael Roth <michael.roth@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Joerg Roedel <jroedel@...e.de>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        linux-kbuild@...r.kernel.org
Subject: [PATCH 2/4] kexec: add CONFING_KEXEC_PURGATORY_SKIP_SIG

From: "huangjie.albert" <huangjie.albert@...edance.com>

the verify_sha256_digest may cost 300+ ms in my test environment:
bzImage: 53M initramfs:28M

We can add a macro to control whether to enable this check. If we
can confirm that the data in this will not change, we can turn off
the check and get a faster startup.

Signed-off-by: huangjie.albert <huangjie.albert@...edance.com>
---
 arch/x86/Kconfig               | 9 +++++++++
 arch/x86/purgatory/purgatory.c | 7 +++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 52a7f91527fe..adbd3a2bd60f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2052,6 +2052,15 @@ config KEXEC_BZIMAGE_VERIFY_SIG
 	help
 	  Enable bzImage signature verification support.
 
+config KEXEC_PURGATORY_SKIP_SIG
+	bool "skip kexec purgatory signature verification"
+	depends on ARCH_HAS_KEXEC_PURGATORY
+	help
+	  this options makes the kexec purgatory do  not signature verification
+	  which would get hundreds of milliseconds saved during kexec boot. If we can
+	  confirm that the data of each segment loaded by kexec will not change we may
+	  enable this option
+
 config CRASH_DUMP
 	bool "kernel crash dumps"
 	depends on X86_64 || (X86_32 && HIGHMEM)
diff --git a/arch/x86/purgatory/purgatory.c b/arch/x86/purgatory/purgatory.c
index 7558139920f8..b3f15774d86d 100644
--- a/arch/x86/purgatory/purgatory.c
+++ b/arch/x86/purgatory/purgatory.c
@@ -20,6 +20,12 @@ u8 purgatory_sha256_digest[SHA256_DIGEST_SIZE] __section(".kexec-purgatory");
 
 struct kexec_sha_region purgatory_sha_regions[KEXEC_SEGMENT_MAX] __section(".kexec-purgatory");
 
+#ifdef CONFIG_KEXEC_PURGATORY_SKIP_SIG
+static int verify_sha256_digest(void)
+{
+	return 0;
+}
+#else
 static int verify_sha256_digest(void)
 {
 	struct kexec_sha_region *ptr, *end;
@@ -39,6 +45,7 @@ static int verify_sha256_digest(void)
 
 	return 0;
 }
+#endif
 
 void purgatory(void)
 {
-- 
2.31.1