diff mbox series

[2/4] kexec: add CONFING_KEXEC_PURGATORY_SKIP_SIG

Message ID 20220725083904.56552-3-huangjie.albert@bytedance.com (mailing list archive)
State New, archived
Headers show
Series faster kexec reboot | expand

Commit Message

黄杰 July 25, 2022, 8:38 a.m. UTC 
From: "huangjie.albert" <huangjie.albert@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@bytedance.com>
---
 arch/x86/Kconfig               | 9 +++++++++
 arch/x86/purgatory/purgatory.c | 7 +++++++
 2 files changed, 16 insertions(+)

Comments

Jason A. Donenfeld July 25, 2022, 12:15 p.m. UTC | #1 
Hi Albert,

On Mon, Jul 25, 2022 at 04:38:54PM +0800, Albert Huang wrote:
> +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
> +

Some grammar nits here, but actually, wouldn't it be better to make this
depend on some other signature things instead? Like if the parent kernel
actually did a big signature computation, then maybe the purgatory step
is needed, but if it didn't bother, then maybe you can skip it. This
way, you don't need a compile-time option that might change some aspect
of signature verification people might otherwise be relying on.

Jason
黄杰 July 25, 2022, 1:32 p.m. UTC | #2 
maybe a boot parameter ?

Jason A. Donenfeld <Jason@zx2c4.com> 于2022年7月25日周一 20:15写道：
>
> Hi Albert,
>
> On Mon, Jul 25, 2022 at 04:38:54PM +0800, Albert Huang wrote:
> > +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
> > +
>
> Some grammar nits here, but actually, wouldn't it be better to make this
> depend on some other signature things instead? Like if the parent kernel
> actually did a big signature computation, then maybe the purgatory step
> is needed, but if it didn't bother, then maybe you can skip it. This
> way, you don't need a compile-time option that might change some aspect
> of signature verification people might otherwise be relying on.
>
> Jason
黄杰 July 28, 2022, 1:57 a.m. UTC | #3 
Does anyone know why this sha256 checksum is put here? I feel that it
is better to put it in the system call of kexec -e.
If the verification is not passed, the second kernel will not be
started, and some prompt information will be printed at the
same time, which seems to be better than when the second kernel is
started. Doing the verification operation will be more friendly,
 and it can also reduce downtime.

黄杰 <huangjie.albert@bytedance.com> 于2022年7月25日周一 21:32写道：
>
> maybe a boot parameter ?
>
> Jason A. Donenfeld <Jason@zx2c4.com> 于2022年7月25日周一 20:15写道：
> >
> > Hi Albert,
> >
> > On Mon, Jul 25, 2022 at 04:38:54PM +0800, Albert Huang wrote:
> > > +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
> > > +
> >
> > Some grammar nits here, but actually, wouldn't it be better to make this
> > depend on some other signature things instead? Like if the parent kernel
> > actually did a big signature computation, then maybe the purgatory step
> > is needed, but if it didn't bother, then maybe you can skip it. This
> > way, you don't need a compile-time option that might change some aspect
> > of signature verification people might otherwise be relying on.
> >
> > Jason
diff mbox series

Patch

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)
 {