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* [PATCH v4 1/3] m68k: process bootinfo records before saving them
@ 2022-09-26 11:37 Jason A. Donenfeld
  2022-09-26 11:37 ` [PATCH v4 2/3] m68k: rework BI_VIRT_RNG_SEED as BI_RNG_SEED Jason A. Donenfeld
  2022-09-26 11:37 ` [PATCH v4 3/3] m68k: generate new RNG seed on reboot Jason A. Donenfeld
  0 siblings, 2 replies; 5+ messages in thread
From: Jason A. Donenfeld @ 2022-09-26 11:37 UTC (permalink / raw)
  To: Geert Uytterhoeven, linux-m68k, linux-kernel
  Cc: Jason A. Donenfeld, Geert Uytterhoeven

The RNG seed boot record is memzeroed after processing, in order to
preserve forward secrecy. By saving the bootinfo for procfs prior to
that, forward secrecy is violated, since it becomes possible to recover
past states. So, save the bootinfo block only after first processing
them.

Fixes: a1ee38ab1a75 ("m68k: virt: Use RNG seed from bootinfo block")
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 arch/m68k/kernel/setup_mm.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/m68k/kernel/setup_mm.c b/arch/m68k/kernel/setup_mm.c
index e62fa8f2149b..7e7ef67cff8b 100644
--- a/arch/m68k/kernel/setup_mm.c
+++ b/arch/m68k/kernel/setup_mm.c
@@ -109,10 +109,9 @@ extern void paging_init(void);
 
 static void __init m68k_parse_bootinfo(const struct bi_record *record)
 {
+	const struct bi_record *first_record = record;
 	uint16_t tag;
 
-	save_bootinfo(record);
-
 	while ((tag = be16_to_cpu(record->tag)) != BI_LAST) {
 		int unknown = 0;
 		const void *data = record->data;
@@ -182,6 +181,8 @@ static void __init m68k_parse_bootinfo(const struct bi_record *record)
 		record = (struct bi_record *)((unsigned long)record + size);
 	}
 
+	save_bootinfo(first_record);
+
 	m68k_realnum_memory = m68k_num_memory;
 #ifdef CONFIG_SINGLE_MEMORY_CHUNK
 	if (m68k_num_memory > 1) {
-- 
2.37.3


^ permalink raw reply related	[flat|nested] 5+ messages in thread

* [PATCH v4 2/3] m68k: rework BI_VIRT_RNG_SEED as BI_RNG_SEED
  2022-09-26 11:37 [PATCH v4 1/3] m68k: process bootinfo records before saving them Jason A. Donenfeld
@ 2022-09-26 11:37 ` Jason A. Donenfeld
  2022-09-26 11:37 ` [PATCH v4 3/3] m68k: generate new RNG seed on reboot Jason A. Donenfeld
  1 sibling, 0 replies; 5+ messages in thread
From: Jason A. Donenfeld @ 2022-09-26 11:37 UTC (permalink / raw)
  To: Geert Uytterhoeven, linux-m68k, linux-kernel
  Cc: Jason A. Donenfeld, Laurent Vivier

This is useful on !virt platforms for kexec, so change things from
BI_VIRT_RNG_SEED to be BI_RNG_SEED, and simply remove BI_VIRT_RNG_SEED
because it only ever lasted one release, and nothing is broken by not
having it. At the same time, keep a comment noting that it's been
removed, so that ID isn't reused. In addition, we previously documented
2-byte alignment, but 4-byte alignment is actually necessary, so update
that comment.

Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Laurent Vivier <laurent@vivier.eu>
Fixes: a1ee38ab1a75 ("m68k: virt: Use RNG seed from bootinfo block")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 arch/m68k/include/uapi/asm/bootinfo-virt.h |  9 ++-------
 arch/m68k/include/uapi/asm/bootinfo.h      |  8 +++++++-
 arch/m68k/kernel/setup_mm.c                | 12 ++++++++++++
 arch/m68k/virt/config.c                    | 11 -----------
 4 files changed, 21 insertions(+), 19 deletions(-)

diff --git a/arch/m68k/include/uapi/asm/bootinfo-virt.h b/arch/m68k/include/uapi/asm/bootinfo-virt.h
index b091ee9b06e0..7dbcd7bec103 100644
--- a/arch/m68k/include/uapi/asm/bootinfo-virt.h
+++ b/arch/m68k/include/uapi/asm/bootinfo-virt.h
@@ -13,13 +13,8 @@
 #define BI_VIRT_VIRTIO_BASE	0x8004
 #define BI_VIRT_CTRL_BASE	0x8005
 
-/*
- * A random seed used to initialize the RNG. Record format:
- *
- *   - length       [ 2 bytes, 16-bit big endian ]
- *   - seed data    [ `length` bytes, padded to preserve 2-byte alignment ]
- */
-#define BI_VIRT_RNG_SEED	0x8006
+/* No longer used -- replaced with BI_RNG_SEED -- but don't reuse this index:
+ * #define BI_VIRT_RNG_SEED	0x8006 */
 
 #define VIRT_BOOTI_VERSION	MK_BI_VERSION(2, 0)
 
diff --git a/arch/m68k/include/uapi/asm/bootinfo.h b/arch/m68k/include/uapi/asm/bootinfo.h
index 95ecf3ae4c49..6ce7644ab3d6 100644
--- a/arch/m68k/include/uapi/asm/bootinfo.h
+++ b/arch/m68k/include/uapi/asm/bootinfo.h
@@ -64,7 +64,13 @@ struct mem_info {
 					/* (struct mem_info) */
 #define BI_COMMAND_LINE		0x0007	/* kernel command line parameters */
 					/* (string) */
-
+/*
+ * A random seed used to initialize the RNG. Record format:
+ *
+ *   - length       [ 2 bytes, 16-bit big endian ]
+ *   - seed data    [ `length` bytes, padded to preserve 4-byte struct alignment ]
+ */
+#define BI_RNG_SEED		0x0008
 
     /*
      *  Linux/m68k Architectures (BI_MACHTYPE)
diff --git a/arch/m68k/kernel/setup_mm.c b/arch/m68k/kernel/setup_mm.c
index 7e7ef67cff8b..e45cc9923703 100644
--- a/arch/m68k/kernel/setup_mm.c
+++ b/arch/m68k/kernel/setup_mm.c
@@ -25,6 +25,7 @@
 #include <linux/module.h>
 #include <linux/nvram.h>
 #include <linux/initrd.h>
+#include <linux/random.h>
 
 #include <asm/bootinfo.h>
 #include <asm/byteorder.h>
@@ -151,6 +152,17 @@ static void __init m68k_parse_bootinfo(const struct bi_record *record)
 				sizeof(m68k_command_line));
 			break;
 
+		case BI_RNG_SEED: {
+			u16 len = be16_to_cpup(data);
+			add_bootloader_randomness(data + 2, len);
+			/*
+			 * Zero the data to preserve forward secrecy, and zero the
+			 * length to prevent kexec from using it.
+			 */
+			memzero_explicit((void *)data, len + 2);
+			break;
+		}
+
 		default:
 			if (MACH_IS_AMIGA)
 				unknown = amiga_parse_bootinfo(record);
diff --git a/arch/m68k/virt/config.c b/arch/m68k/virt/config.c
index 4ab22946ff68..632ba200ad42 100644
--- a/arch/m68k/virt/config.c
+++ b/arch/m68k/virt/config.c
@@ -2,7 +2,6 @@
 
 #include <linux/reboot.h>
 #include <linux/serial_core.h>
-#include <linux/random.h>
 #include <clocksource/timer-goldfish.h>
 
 #include <asm/bootinfo.h>
@@ -93,16 +92,6 @@ int __init virt_parse_bootinfo(const struct bi_record *record)
 		data += 4;
 		virt_bi_data.virtio.irq = be32_to_cpup(data);
 		break;
-	case BI_VIRT_RNG_SEED: {
-		u16 len = be16_to_cpup(data);
-		add_bootloader_randomness(data + 2, len);
-		/*
-		 * Zero the data to preserve forward secrecy, and zero the
-		 * length to prevent kexec from using it.
-		 */
-		memzero_explicit((void *)data, len + 2);
-		break;
-	}
 	default:
 		unknown = 1;
 		break;
-- 
2.37.3


^ permalink raw reply related	[flat|nested] 5+ messages in thread

* [PATCH v4 3/3] m68k: generate new RNG seed on reboot
  2022-09-26 11:37 [PATCH v4 1/3] m68k: process bootinfo records before saving them Jason A. Donenfeld
  2022-09-26 11:37 ` [PATCH v4 2/3] m68k: rework BI_VIRT_RNG_SEED as BI_RNG_SEED Jason A. Donenfeld
@ 2022-09-26 11:37 ` Jason A. Donenfeld
  2022-09-26 13:13   ` Jason A. Donenfeld
  1 sibling, 1 reply; 5+ messages in thread
From: Jason A. Donenfeld @ 2022-09-26 11:37 UTC (permalink / raw)
  To: Geert Uytterhoeven, linux-m68k, linux-kernel; +Cc: Jason A. Donenfeld

Rather than rebooting into a system with no entropy, regenerate the RNG
seed before rebooting, so that the new system has a fresh seed.

Fixes: a1ee38ab1a75 ("m68k: virt: Use RNG seed from bootinfo block")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 arch/m68k/include/asm/bootinfo.h |  2 ++
 arch/m68k/kernel/process.c       | 11 +++++++++++
 arch/m68k/kernel/setup_mm.c      |  2 ++
 3 files changed, 15 insertions(+)

diff --git a/arch/m68k/include/asm/bootinfo.h b/arch/m68k/include/asm/bootinfo.h
index 81c91af8ec6c..71103530839a 100644
--- a/arch/m68k/include/asm/bootinfo.h
+++ b/arch/m68k/include/asm/bootinfo.h
@@ -28,6 +28,8 @@ void process_uboot_commandline(char *commandp, int size);
 static inline void process_uboot_commandline(char *commandp, int size) {}
 #endif
 
+extern const struct bi_record *rng_seed_record;
+
 #endif /* __ASSEMBLY__ */
 
 
diff --git a/arch/m68k/kernel/process.c b/arch/m68k/kernel/process.c
index 2cb4a61bcfac..c2b20d5d51e2 100644
--- a/arch/m68k/kernel/process.c
+++ b/arch/m68k/kernel/process.c
@@ -29,6 +29,7 @@
 #include <linux/reboot.h>
 #include <linux/init_task.h>
 #include <linux/mqueue.h>
+#include <linux/random.h>
 #include <linux/rcupdate.h>
 #include <linux/syscalls.h>
 #include <linux/uaccess.h>
@@ -36,6 +37,7 @@
 #include <asm/traps.h>
 #include <asm/machdep.h>
 #include <asm/setup.h>
+#include <asm/bootinfo.h>
 
 
 asmlinkage void ret_from_fork(void);
@@ -51,8 +53,17 @@ void arch_cpu_idle(void)
 #endif
 }
 
+const struct bi_record *rng_seed_record;
+
 void machine_restart(char * __unused)
 {
+	if (rng_seed_record && rng_seed_record->size > sizeof(*rng_seed_record) + 2) {
+		u16 len = rounddown_pow_of_two(rng_seed_record->size -
+					       sizeof(*rng_seed_record) - 2);
+		get_random_bytes((u8 *)rng_seed_record->data + 2, len);
+		*(u16 *)rng_seed_record->data = cpu_to_be16(len);
+	}
+
 	if (mach_reset)
 		mach_reset();
 	for (;;);
diff --git a/arch/m68k/kernel/setup_mm.c b/arch/m68k/kernel/setup_mm.c
index e45cc9923703..eacf734bea0e 100644
--- a/arch/m68k/kernel/setup_mm.c
+++ b/arch/m68k/kernel/setup_mm.c
@@ -160,6 +160,8 @@ static void __init m68k_parse_bootinfo(const struct bi_record *record)
 			 * length to prevent kexec from using it.
 			 */
 			memzero_explicit((void *)data, len + 2);
+			/* Store a reference to be filled in on reboot. */
+			rng_seed_record = record;
 			break;
 		}
 
-- 
2.37.3


^ permalink raw reply related	[flat|nested] 5+ messages in thread

* Re: [PATCH v4 3/3] m68k: generate new RNG seed on reboot
  2022-09-26 11:37 ` [PATCH v4 3/3] m68k: generate new RNG seed on reboot Jason A. Donenfeld
@ 2022-09-26 13:13   ` Jason A. Donenfeld
  2022-09-27 13:09     ` Jason A. Donenfeld
  0 siblings, 1 reply; 5+ messages in thread
From: Jason A. Donenfeld @ 2022-09-26 13:13 UTC (permalink / raw)
  To: Geert Uytterhoeven, linux-m68k, linux-kernel, Laurent Vivier

Hi Geert,

On Mon, Sep 26, 2022 at 1:38 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> Rather than rebooting into a system with no entropy, regenerate the RNG
> seed before rebooting, so that the new system has a fresh seed.
>
> Fixes: a1ee38ab1a75 ("m68k: virt: Use RNG seed from bootinfo block")
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Laurent made a compelling case *against* this approach. So feel free
to drop this 3/3 patch. However, 1/3 and 2/3 should still be
committed.

Thanks,
Jason

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH v4 3/3] m68k: generate new RNG seed on reboot
  2022-09-26 13:13   ` Jason A. Donenfeld
@ 2022-09-27 13:09     ` Jason A. Donenfeld
  0 siblings, 0 replies; 5+ messages in thread
From: Jason A. Donenfeld @ 2022-09-27 13:09 UTC (permalink / raw)
  To: Geert Uytterhoeven, linux-m68k, linux-kernel, Laurent Vivier

On Mon, Sep 26, 2022 at 03:13:01PM +0200, Jason A. Donenfeld wrote:
> Hi Geert,
> 
> On Mon, Sep 26, 2022 at 1:38 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> >
> > Rather than rebooting into a system with no entropy, regenerate the RNG
> > seed before rebooting, so that the new system has a fresh seed.
> >
> > Fixes: a1ee38ab1a75 ("m68k: virt: Use RNG seed from bootinfo block")
> > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> 
> Laurent made a compelling case *against* this approach. So feel free
> to drop this 3/3 patch. However, 1/3 and 2/3 should still be
> committed.

For Geert's ease, I'll send a v5 with 3/3 dropped.

Jason

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2022-09-27 13:10 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-09-26 11:37 [PATCH v4 1/3] m68k: process bootinfo records before saving them Jason A. Donenfeld
2022-09-26 11:37 ` [PATCH v4 2/3] m68k: rework BI_VIRT_RNG_SEED as BI_RNG_SEED Jason A. Donenfeld
2022-09-26 11:37 ` [PATCH v4 3/3] m68k: generate new RNG seed on reboot Jason A. Donenfeld
2022-09-26 13:13   ` Jason A. Donenfeld
2022-09-27 13:09     ` Jason A. Donenfeld

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