[PATCH 2/4] kexec: add CONFING_KEXEC_PURGATORY_SKIP_SIG

[Albert Huang]

From: "huangjie.albert" <huangjie.albert at bytedance.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 at bytedance.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