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hw/i386: pass RNG seed via setup_data entry

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Tiny machines optimized for fast boot time generally don't use EFI,
which means a random seed has to be supplied some other way. For this
purpose, Linux (≥5.20) supports passing a seed in the setup_data table
with SETUP_RNG_SEED, specially intended for hypervisors, kexec, and
specialized bootloaders. The linked commit shows the upstream kernel
implementation.

At Paolo's request, we don't pass these to versioned machine types ≤7.0.

Link: https://git.kernel.org/tip/tip/c/68b8e9713c8
Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Eduardo Habkost <eduardo@habkost.net>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
Cc: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Message-Id: <20220721125636.446842-1-Jason@zx2c4.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Jason A. Donenfeld 2022-07-21 14:56:36 +02:00 committed by Paolo Bonzini
parent c287941a4d
commit 67f7e426e5
8 changed files with 35 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
hw/i386/microvm.c
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@ -332,7 +332,7 @@ static void microvm_memory_init(MicrovmMachineState *mms)
rom_set_fw(fw_cfg);
if (machine->kernel_filename != NULL) {
x86_load_linux(x86ms, fw_cfg, 0, true);
x86_load_linux(x86ms, fw_cfg, 0, true, false);
}
if (mms->option_roms) {

4
hw/i386/pc.c
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@ -796,7 +796,7 @@ void xen_load_linux(PCMachineState *pcms)
rom_set_fw(fw_cfg);
x86_load_linux(x86ms, fw_cfg, pcmc->acpi_data_size,
pcmc->pvh_enabled);
pcmc->pvh_enabled, pcmc->legacy_no_rng_seed);
for (i = 0; i < nb_option_roms; i++) {
assert(!strcmp(option_rom[i].name, "linuxboot.bin") ||
!strcmp(option_rom[i].name, "linuxboot_dma.bin") ||
@ -992,7 +992,7 @@ void pc_memory_init(PCMachineState *pcms,
if (linux_boot) {
x86_load_linux(x86ms, fw_cfg, pcmc->acpi_data_size,
pcmc->pvh_enabled);
pcmc->pvh_enabled, pcmc->legacy_no_rng_seed);
}
for (i = 0; i < nb_option_roms; i++) {

2
hw/i386/pc_piix.c
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@ -438,9 +438,11 @@ DEFINE_I440FX_MACHINE(v7_1, "pc-i440fx-7.1", NULL,
static void pc_i440fx_7_0_machine_options(MachineClass *m)
{
PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
pc_i440fx_7_1_machine_options(m);
m->alias = NULL;
m->is_default = false;
pcmc->legacy_no_rng_seed = true;
compat_props_add(m->compat_props, hw_compat_7_0, hw_compat_7_0_len);
compat_props_add(m->compat_props, pc_compat_7_0, pc_compat_7_0_len);
}

2
hw/i386/pc_q35.c
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@ -375,8 +375,10 @@ DEFINE_Q35_MACHINE(v7_1, "pc-q35-7.1", NULL,
static void pc_q35_7_0_machine_options(MachineClass *m)
{
PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
pc_q35_7_1_machine_options(m);
m->alias = NULL;
pcmc->legacy_no_rng_seed = true;
compat_props_add(m->compat_props, hw_compat_7_0, hw_compat_7_0_len);
compat_props_add(m->compat_props, pc_compat_7_0, pc_compat_7_0_len);
}

26
hw/i386/x86.c
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@ -26,6 +26,7 @@
#include "qemu/cutils.h"
#include "qemu/units.h"
#include "qemu/datadir.h"
#include "qemu/guest-random.h"
#include "qapi/error.h"
#include "qapi/qmp/qerror.h"
#include "qapi/qapi-visit-common.h"
@ -766,7 +767,8 @@ static bool load_elfboot(const char *kernel_filename,
void x86_load_linux(X86MachineState *x86ms,
FWCfgState *fw_cfg,
int acpi_data_size,
bool pvh_enabled)
bool pvh_enabled,
bool legacy_no_rng_seed)
{
bool linuxboot_dma_enabled = X86_MACHINE_GET_CLASS(x86ms)->fwcfg_dma_enabled;
uint16_t protocol;
@ -774,7 +776,7 @@ void x86_load_linux(X86MachineState *x86ms,
int dtb_size, setup_data_offset;
uint32_t initrd_max;
uint8_t header[8192], *setup, *kernel;
hwaddr real_addr, prot_addr, cmdline_addr, initrd_addr = 0;
hwaddr real_addr, prot_addr, cmdline_addr, initrd_addr = 0, first_setup_data = 0;
FILE *f;
char *vmode;
MachineState *machine = MACHINE(x86ms);
@ -784,6 +786,7 @@ void x86_load_linux(X86MachineState *x86ms,
const char *dtb_filename = machine->dtb;
const char *kernel_cmdline = machine->kernel_cmdline;
SevKernelLoaderContext sev_load_ctx = {};
enum { RNG_SEED_LENGTH = 32 };
/* Align to 16 bytes as a paranoia measure */
cmdline_size = (strlen(kernel_cmdline) + 16) & ~15;
@ -1063,16 +1066,31 @@ void x86_load_linux(X86MachineState *x86ms,
kernel_size = setup_data_offset + sizeof(struct setup_data) + dtb_size;
kernel = g_realloc(kernel, kernel_size);
stq_p(header + 0x250, prot_addr + setup_data_offset);
setup_data = (struct setup_data *)(kernel + setup_data_offset);
setup_data->next = 0;
setup_data->next = cpu_to_le64(first_setup_data);
first_setup_data = prot_addr + setup_data_offset;
setup_data->type = cpu_to_le32(SETUP_DTB);
setup_data->len = cpu_to_le32(dtb_size);
load_image_size(dtb_filename, setup_data->data, dtb_size);
}
if (!legacy_no_rng_seed) {
setup_data_offset = QEMU_ALIGN_UP(kernel_size, 16);
kernel_size = setup_data_offset + sizeof(struct setup_data) + RNG_SEED_LENGTH;
kernel = g_realloc(kernel, kernel_size);
setup_data = (struct setup_data *)(kernel + setup_data_offset);
setup_data->next = cpu_to_le64(first_setup_data);
first_setup_data = prot_addr + setup_data_offset;
setup_data->type = cpu_to_le32(SETUP_RNG_SEED);
setup_data->len = cpu_to_le32(RNG_SEED_LENGTH);
qemu_guest_getrandom_nofail(setup_data->data, RNG_SEED_LENGTH);
}
/* Offset 0x250 is a pointer to the first setup_data link. */
stq_p(header + 0x250, first_setup_data);
/*
* If we're starting an encrypted VM, it will be OVMF based, which uses the
* efi stub for booting and doesn't require any values to be placed in the

3
include/hw/i386/pc.h
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@ -127,6 +127,9 @@ struct PCMachineClass {
/* create kvmclock device even when KVM PV features are not exposed */
bool kvmclock_create_always;
/* skip passing an rng seed for legacy machines */
bool legacy_no_rng_seed;
};
#define TYPE_PC_MACHINE "generic-pc-machine"

3
include/hw/i386/x86.h
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@ -123,7 +123,8 @@ void x86_bios_rom_init(MachineState *ms, const char *default_firmware,
void x86_load_linux(X86MachineState *x86ms,
FWCfgState *fw_cfg,
int acpi_data_size,
bool pvh_enabled);
bool pvh_enabled,
bool legacy_no_rng_seed);
bool x86_machine_is_smm_enabled(const X86MachineState *x86ms);
bool x86_machine_is_acpi_enabled(const X86MachineState *x86ms);

1
include/standard-headers/asm-x86/bootparam.h
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@ -10,6 +10,7 @@
#define SETUP_EFI 4
#define SETUP_APPLE_PROPERTIES 5
#define SETUP_JAILHOUSE 6
#define SETUP_RNG_SEED 9
#define SETUP_INDIRECT (1<<31)