On Wed, 2023-02-01 at 15:48 -0500, Jason A. Donenfeld wrote:
[...]
> But it sounds like you might now have a concrete suggestion on
> something even better. I'm CCing hpa, as this is his wheelhouse, and
> maybe you two can divise the next step while I'm away. Maybe the pad9
> thing you mentioned is the super nice solution we've been searching
> for this whole time. When I'm home in 10 days and have internet
> again, I'll take a look at where thing's are out and try to figure
> out how I can be productive again with it.
OK, so just FYI HPA, this is the patch I'm thinking of sending to
linux-kernel to reserve space in struct boot_params for this. If you
could take a look and advise on the location before I send the final
patch, I'd be grateful. I took space in _pad9 because that's the
standard method (add on to end), but it does strike me we could also
use all of _pad8 for the (the addition is only 48 bytes) or even _pad3
+ hd0_info + hd1_info.
James
---
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 9338c68e7413..0120ab77dac9 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -308,7 +308,7 @@ _start:
# Part 2 of the header, from the old setup.S
.ascii "HdrS" # header signature
- .word 0x020f # header version number (>= 0x0105)
+ .word 0x0210 # header version number (>= 0x0105)
# or else old loadlin-1.5 will fail)
.globl realmode_swtch
realmode_swtch: .word 0, 0 # default_switch, SETUPSEG
diff --git a/arch/x86/include/uapi/asm/bootparam.h
b/arch/x86/include/uapi/asm/bootparam.h
index 01d19fc22346..c614ff0755f2 100644
--- a/arch/x86/include/uapi/asm/bootparam.h
+++ b/arch/x86/include/uapi/asm/bootparam.h
@@ -181,6 +181,19 @@ struct ima_setup_data {
__u64 size;
} __attribute__((packed));
+/*
+ * Define a boot_param area for the RNG seed which can be used via the
+ * setup_data mechanism (so must have a setup_data header) but which
+ * is embedded in boot_params because qemu has been unable to find
+ * a safe data space for it. The value RNG_SEED_LENGTH must not
+ * change (pad length dependent on it) and must match the value in QEMU
+ */
+#define RNG_SEED_LENGTH 32
+struct random_seed_data {
+ struct setup_data s;
+ __u8 data[RNG_SEED_LENGTH];
+} __attribute__((packed));
+
/* The so-called "zeropage" */
struct boot_params {
struct screen_info screen_info; /* 0x000 */
@@ -228,7 +241,8 @@ struct boot_params {
struct boot_e820_entry e820_table[E820_MAX_ENTRIES_ZEROPAGE]; /* 0x2d0
*/
__u8 _pad8[48]; /* 0xcd0 */
struct edd_info eddbuf[EDDMAXNR]; /* 0xd00 */
- __u8 _pad9[276]; /* 0xeec */
+ struct random_seed_data random_seed; /* 0xeec */
+ __u8 _pad9[228]; /* 0xf1c */
} __attribute__((packed));
/**
diff --git a/arch/x86/kernel/kexec-bzimage64.c
b/arch/x86/kernel/kexec-bzimage64.c
index 6b58610a1552..fb719682579d 100644
--- a/arch/x86/kernel/kexec-bzimage64.c
+++ b/arch/x86/kernel/kexec-bzimage64.c
@@ -110,13 +110,10 @@ static int setup_e820_entries(struct boot_params *params)
return 0;
}
-enum { RNG_SEED_LENGTH = 32 };
-
static void
-setup_rng_seed(struct boot_params *params, unsigned long params_load_addr,
- unsigned int rng_seed_setup_data_offset)
+setup_rng_seed(struct boot_params *params, unsigned long params_load_addr)
{
- struct setup_data *sd = (void *)params + rng_seed_setup_data_offset;
+ struct setup_data *sd = ¶ms->random_seed.s;
unsigned long setup_data_phys;
if (!rng_is_initialized())
@@ -125,7 +122,8 @@ setup_rng_seed(struct boot_params *params, unsigned long
params_load_addr,
sd->type = SETUP_RNG_SEED;
sd->len = RNG_SEED_LENGTH;
get_random_bytes(sd->data, RNG_SEED_LENGTH);
- setup_data_phys = params_load_addr + rng_seed_setup_data_offset;
+ setup_data_phys = params_load_addr + offsetof(struct boot_params,
+ random_seed);
sd->next = params->hdr.setup_data;
params->hdr.setup_data = setup_data_phys;
}
@@ -306,7 +304,7 @@ setup_boot_parameters(struct kimage *image, struct
boot_params *params,
}
/* Setup RNG seed */
- setup_rng_seed(params, params_load_addr, setup_data_offset);
+ setup_rng_seed(params, params_load_addr);
/* Setup EDD info */
memcpy(params->eddbuf, boot_params.eddbuf,
