Re: [PATCH] x86: temporarily remove all attempts to provide setup_data

From: Nathan Chancellor
Date: Wed Feb 08 2023 - 13:14:27 EST


On Wed, Feb 08, 2023 at 03:08:35PM -0300, Jason A. Donenfeld wrote:
> All attempts at providing setup_data have been made as an iteration on
> whatever was there before, stretching back to the original
> implementation used for DTBs that [mis]used the kernel image itself.
> We've now had a dozen rounds of bugs and hacks, and the result is
> turning into a pile of unmaintainable and increasingly brittle hacks.
>
> Let's just rip out all the madness and start over. We can re-architect
> this based on having a separate standalone setup_data file, which is how
> it should have been done in the first place. This is a larger project
> with a few things to coordinate, but we can't really begin thinking
> about that while trying to play whack-a-mole with the current buggy
> implementation.
>
> So this commit removes the setup_data setting from x86_load_linux(),
> while leaving intact the infrastructure we'll need in the future to try
> again.
>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Dov Murik <dovmurik@xxxxxxxxxxxxx>
> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> Cc: Daniel P. Berrangé <berrange@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Richard Henderson <richard.henderson@xxxxxxxxxx>
> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> Cc: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
> Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>

Thanks for the quick patch! Both of my use cases appear fixed.

Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>

> ---
> hw/i386/microvm.c | 15 ++----
> hw/i386/x86.c | 120 +++++-----------------------------------------
> 2 files changed, 17 insertions(+), 118 deletions(-)
>
> diff --git a/hw/i386/microvm.c b/hw/i386/microvm.c
> index 29f30dd6d3..170a331e3f 100644
> --- a/hw/i386/microvm.c
> +++ b/hw/i386/microvm.c
> @@ -378,8 +378,7 @@ static void microvm_fix_kernel_cmdline(MachineState *machine)
> MicrovmMachineState *mms = MICROVM_MACHINE(machine);
> BusState *bus;
> BusChild *kid;
> - char *cmdline, *existing_cmdline;
> - size_t len;
> + char *cmdline;
>
> /*
> * Find MMIO transports with attached devices, and add them to the kernel
> @@ -388,8 +387,7 @@ static void microvm_fix_kernel_cmdline(MachineState *machine)
> * Yes, this is a hack, but one that heavily improves the UX without
> * introducing any significant issues.
> */
> - existing_cmdline = fw_cfg_read_bytes_ptr(x86ms->fw_cfg, FW_CFG_CMDLINE_DATA);
> - cmdline = g_strdup(existing_cmdline);
> + cmdline = g_strdup(machine->kernel_cmdline);
> bus = sysbus_get_default();
> QTAILQ_FOREACH(kid, &bus->children, sibling) {
> DeviceState *dev = kid->child;
> @@ -413,12 +411,9 @@ static void microvm_fix_kernel_cmdline(MachineState *machine)
> }
> }
>
> - len = strlen(cmdline);
> - if (len > VIRTIO_CMDLINE_TOTAL_MAX_LEN + strlen(existing_cmdline)) {
> - fprintf(stderr, "qemu: virtio mmio cmdline too large, skipping\n");
> - } else {
> - memcpy(existing_cmdline, cmdline, len + 1);
> - }
> + fw_cfg_modify_i32(x86ms->fw_cfg, FW_CFG_CMDLINE_SIZE, strlen(cmdline) + 1);
> + fw_cfg_modify_string(x86ms->fw_cfg, FW_CFG_CMDLINE_DATA, cmdline);
> +
> g_free(cmdline);
> }
>
> diff --git a/hw/i386/x86.c b/hw/i386/x86.c
> index eaff4227bd..6cfdca9acd 100644
> --- a/hw/i386/x86.c
> +++ b/hw/i386/x86.c
> @@ -50,7 +50,6 @@
> #include "hw/intc/i8259.h"
> #include "hw/rtc/mc146818rtc.h"
> #include "target/i386/sev.h"
> -#include "hw/i386/microvm.h"
>
> #include "hw/acpi/cpu_hotplug.h"
> #include "hw/irq.h"
> @@ -770,30 +769,6 @@ static bool load_elfboot(const char *kernel_filename,
> return true;
> }
>
> -typedef struct SetupDataFixup {
> - void *pos;
> - hwaddr orig_val, new_val;
> - uint32_t addr;
> -} SetupDataFixup;
> -
> -static void fixup_setup_data(void *opaque)
> -{
> - SetupDataFixup *fixup = opaque;
> - stq_p(fixup->pos, fixup->new_val);
> -}
> -
> -static void reset_setup_data(void *opaque)
> -{
> - SetupDataFixup *fixup = opaque;
> - stq_p(fixup->pos, fixup->orig_val);
> -}
> -
> -static void reset_rng_seed(void *opaque)
> -{
> - SetupData *setup_data = opaque;
> - qemu_guest_getrandom_nofail(setup_data->data, le32_to_cpu(setup_data->len));
> -}
> -
> void x86_load_linux(X86MachineState *x86ms,
> FWCfgState *fw_cfg,
> int acpi_data_size,
> @@ -803,29 +778,20 @@ void x86_load_linux(X86MachineState *x86ms,
> bool linuxboot_dma_enabled = X86_MACHINE_GET_CLASS(x86ms)->fwcfg_dma_enabled;
> uint16_t protocol;
> int setup_size, kernel_size, cmdline_size;
> - 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, first_setup_data = 0;
> + hwaddr real_addr, prot_addr, cmdline_addr, initrd_addr = 0;
> FILE *f;
> char *vmode;
> MachineState *machine = MACHINE(x86ms);
> - SetupData *setup_data;
> const char *kernel_filename = machine->kernel_filename;
> const char *initrd_filename = machine->initrd_filename;
> - const char *dtb_filename = machine->dtb;
> - char *kernel_cmdline;
> + const char *kernel_cmdline = machine->kernel_cmdline;
> SevKernelLoaderContext sev_load_ctx = {};
> enum { RNG_SEED_LENGTH = 32 };
>
> - /*
> - * Add the NUL terminator, some padding for the microvm cmdline fiddling
> - * hack, and then align to 16 bytes as a paranoia measure
> - */
> - cmdline_size = (strlen(machine->kernel_cmdline) + 1 +
> - VIRTIO_CMDLINE_TOTAL_MAX_LEN + 16) & ~15;
> - /* Make a copy, since we might append arbitrary bytes to it later. */
> - kernel_cmdline = g_strndup(machine->kernel_cmdline, cmdline_size);
> + /* Align to 16 bytes as a paranoia measure */
> + cmdline_size = (strlen(kernel_cmdline) + 16) & ~15;
>
> /* load the kernel header */
> f = fopen(kernel_filename, "rb");
> @@ -966,6 +932,12 @@ void x86_load_linux(X86MachineState *x86ms,
> initrd_max = x86ms->below_4g_mem_size - acpi_data_size - 1;
> }
>
> + fw_cfg_add_i32(fw_cfg, FW_CFG_CMDLINE_ADDR, cmdline_addr);
> + fw_cfg_add_i32(fw_cfg, FW_CFG_CMDLINE_SIZE, strlen(kernel_cmdline) + 1);
> + fw_cfg_add_string(fw_cfg, FW_CFG_CMDLINE_DATA, kernel_cmdline);
> + sev_load_ctx.cmdline_data = (char *)kernel_cmdline;
> + sev_load_ctx.cmdline_size = strlen(kernel_cmdline) + 1;
> +
> if (protocol >= 0x202) {
> stl_p(header + 0x228, cmdline_addr);
> } else {
> @@ -1078,81 +1050,13 @@ void x86_load_linux(X86MachineState *x86ms,
> }
> fclose(f);
>
> - /* append dtb to kernel */
> - if (dtb_filename) {
> - if (protocol < 0x209) {
> - fprintf(stderr, "qemu: Linux kernel too old to load a dtb\n");
> - exit(1);
> - }
> -
> - dtb_size = get_image_size(dtb_filename);
> - if (dtb_size <= 0) {
> - fprintf(stderr, "qemu: error reading dtb %s: %s\n",
> - dtb_filename, strerror(errno));
> - exit(1);
> - }
> -
> - setup_data_offset = cmdline_size;
> - cmdline_size += sizeof(SetupData) + dtb_size;
> - kernel_cmdline = g_realloc(kernel_cmdline, cmdline_size);
> - setup_data = (void *)kernel_cmdline + setup_data_offset;
> - setup_data->next = cpu_to_le64(first_setup_data);
> - first_setup_data = cmdline_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 && protocol >= 0x209) {
> - setup_data_offset = cmdline_size;
> - cmdline_size += sizeof(SetupData) + RNG_SEED_LENGTH;
> - kernel_cmdline = g_realloc(kernel_cmdline, cmdline_size);
> - setup_data = (void *)kernel_cmdline + setup_data_offset;
> - setup_data->next = cpu_to_le64(first_setup_data);
> - first_setup_data = cmdline_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);
> - qemu_register_reset_nosnapshotload(reset_rng_seed, setup_data);
> - fw_cfg_add_bytes_callback(fw_cfg, FW_CFG_KERNEL_DATA, reset_rng_seed, NULL,
> - setup_data, kernel, kernel_size, true);
> - } else {
> - fw_cfg_add_bytes(fw_cfg, FW_CFG_KERNEL_DATA, kernel, kernel_size);
> - }
> -
> - fw_cfg_add_i32(fw_cfg, FW_CFG_CMDLINE_ADDR, cmdline_addr);
> - fw_cfg_add_i32(fw_cfg, FW_CFG_CMDLINE_SIZE, cmdline_size);
> - fw_cfg_add_bytes(fw_cfg, FW_CFG_CMDLINE_DATA, kernel_cmdline, cmdline_size);
> - sev_load_ctx.cmdline_data = (char *)kernel_cmdline;
> - sev_load_ctx.cmdline_size = cmdline_size;
> -
> + fw_cfg_add_bytes(fw_cfg, FW_CFG_KERNEL_DATA, kernel, kernel_size);
> fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_ADDR, prot_addr);
> fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_SIZE, kernel_size);
> sev_load_ctx.kernel_data = (char *)kernel;
> sev_load_ctx.kernel_size = kernel_size;
>
> - /*
> - * 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
> - * kernel header. We therefore don't update the header so the hash of the
> - * kernel on the other side of the fw_cfg interface matches the hash of the
> - * file the user passed in.
> - */
> - if (!sev_enabled() && first_setup_data) {
> - SetupDataFixup *fixup = g_malloc(sizeof(*fixup));
> -
> - memcpy(setup, header, MIN(sizeof(header), setup_size));
> - /* Offset 0x250 is a pointer to the first setup_data link. */
> - fixup->pos = setup + 0x250;
> - fixup->orig_val = ldq_p(fixup->pos);
> - fixup->new_val = first_setup_data;
> - fixup->addr = cpu_to_le32(real_addr);
> - fw_cfg_add_bytes_callback(fw_cfg, FW_CFG_SETUP_ADDR, fixup_setup_data, NULL,
> - fixup, &fixup->addr, sizeof(fixup->addr), true);
> - qemu_register_reset(reset_setup_data, fixup);
> - } else {
> - fw_cfg_add_i32(fw_cfg, FW_CFG_SETUP_ADDR, real_addr);
> - }
> + fw_cfg_add_i32(fw_cfg, FW_CFG_SETUP_ADDR, real_addr);
> fw_cfg_add_i32(fw_cfg, FW_CFG_SETUP_SIZE, setup_size);
> fw_cfg_add_bytes(fw_cfg, FW_CFG_SETUP_DATA, setup, setup_size);
> sev_load_ctx.setup_data = (char *)setup;
> --
> 2.39.1
>