| Message ID | 20200206140352.6300-3-ardb@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arch-agnostic initrd loading method for EFI systems | expand |
On 2/6/20 3:03 PM, Ard Biesheuvel wrote: > One of the advantages of using what basically amounts to a callback > interface into the bootloader for loading the initrd is that it provides > a natural place for the bootloader or firmware to measure the initrd > contents while they are being passed to the kernel. > > Unfortunately, this is not a guarantee that the initrd will in fact be > loaded and its /init invoked by the kernel, since the command line may > contain the 'noinitrd' option, in which case the initrd is ignored, but > this will not be reflected in the PCR that covers the initrd measurement. Does PCR here refer to the TPM Platform Configuration Register? > > This could be addressed by measuring the command line as well, and > including that PCR in the attestation policy, but this locks down the > command line completely, which may be too restrictive. > > So let's take the noinitrd argument into account in the stub, too. This > forces the PCR that covers the initrd to assume a different value when > noinitrd is passed, allowing an attestation policy to disregard the > command line if there is no need to take its measurement into account > for other reasons. > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > --- > drivers/firmware/efi/libstub/arm-stub.c | 23 +++++----- > drivers/firmware/efi/libstub/efi-stub-helper.c | 9 ++++ > drivers/firmware/efi/libstub/efistub.h | 1 + > drivers/firmware/efi/libstub/x86-stub.c | 45 +++++++++++--------- > 4 files changed, 47 insertions(+), 31 deletions(-) > > diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c > index 1db943c1ba2b..5e8f16cf016e 100644 > --- a/drivers/firmware/efi/libstub/arm-stub.c > +++ b/drivers/firmware/efi/libstub/arm-stub.c > @@ -256,18 +256,21 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg, > if (!fdt_addr) > pr_efi("Generating empty DTB\n"); > > - max_addr = efi_get_max_initrd_addr(dram_base, *image_addr); > - status = efi_load_initrd_devpath(&initrd_addr, &initrd_size, max_addr); > - if (status == EFI_SUCCESS) > - pr_efi("Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path\n"); > - else if (status == EFI_NOT_FOUND) { > - status = efi_load_initrd(image, ULONG_MAX, max_addr, > - &initrd_addr, &initrd_size); > + if (!noinitrd()) { > + max_addr = efi_get_max_initrd_addr(dram_base, *image_addr); > + status = efi_load_initrd_devpath(&initrd_addr, &initrd_size, > + max_addr); > if (status == EFI_SUCCESS) > - pr_efi("Loaded initrd from command line option\n"); > + pr_efi("Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path\n"); > + else if (status == EFI_NOT_FOUND) { > + status = efi_load_initrd(image, ULONG_MAX, max_addr, > + &initrd_addr, &initrd_size); > + if (status == EFI_SUCCESS) > + pr_efi("Loaded initrd from command line option\n"); > + } > + if (status != EFI_SUCCESS) > + pr_efi_err("Failed to load initrd!\n"); > } > - if (status != EFI_SUCCESS) > - pr_efi_err("Failed to load initrd!\n"); > > efi_random_get_seed(); > > diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c > index eaf45ea749b3..367575fb8424 100644 > --- a/drivers/firmware/efi/libstub/efi-stub-helper.c > +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c > @@ -11,6 +11,7 @@ > > static bool __efistub_global efi_nochunk; > static bool __efistub_global efi_nokaslr; > +static bool __efistub_global efi_noinitrd; > static bool __efistub_global efi_quiet; > static bool __efistub_global efi_novamap; > static bool __efistub_global efi_nosoftreserve; > @@ -25,6 +26,10 @@ bool __pure nokaslr(void) > { > return efi_nokaslr; > } > +bool __pure noinitrd(void) > +{ > + return efi_noinitrd; > +} > bool __pure is_quiet(void) > { > return efi_quiet; > @@ -71,6 +76,10 @@ efi_status_t efi_parse_options(char const *cmdline) > if (str == cmdline || (str && str > cmdline && *(str - 1) == ' ')) > efi_nokaslr = true; > > + str = strstr(cmdline, "noinitrd"); > + if (str == cmdline || (str && str > cmdline && *(str - 1) == ' ')) > + efi_noinitrd = true; > + > str = strstr(cmdline, "quiet"); > if (str == cmdline || (str && str > cmdline && *(str - 1) == ' ')) > efi_quiet = true; > diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h > index fbf9f9442eed..29a5d0e9554a 100644 > --- a/drivers/firmware/efi/libstub/efistub.h > +++ b/drivers/firmware/efi/libstub/efistub.h > @@ -44,6 +44,7 @@ > > extern bool __pure nochunk(void); > extern bool __pure nokaslr(void); > +extern bool __pure noinitrd(void); > extern bool __pure is_quiet(void); > extern bool __pure novamap(void); > > diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c > index 7f38f95676dd..9d86c0949b3c 100644 > --- a/drivers/firmware/efi/libstub/x86-stub.c > +++ b/drivers/firmware/efi/libstub/x86-stub.c > @@ -419,26 +419,28 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle, > if (status != EFI_SUCCESS) > goto fail2; > > - /* > - * The initrd loaded from the Linux initrd vendor device > - * path should take precedence, as we don't want the > - * [unverified] command line to override the initrd > - * supplied by the [potentially verified] firmware. > - */ > - status = efi_load_initrd_devpath(&ramdisk_addr, &ramdisk_size, > - above4g ? ULONG_MAX > - : hdr->initrd_addr_max); > - if (status == EFI_NOT_FOUND) > - status = efi_load_initrd(image, hdr->initrd_addr_max, > - above4g ? ULONG_MAX > - : hdr->initrd_addr_max, > - &ramdisk_addr, &ramdisk_size); > - if (status != EFI_SUCCESS) > - goto fail2; > - hdr->ramdisk_image = ramdisk_addr & 0xffffffff; > - hdr->ramdisk_size = ramdisk_size & 0xffffffff; > - boot_params->ext_ramdisk_image = (u64)ramdisk_addr >> 32; > - boot_params->ext_ramdisk_size = (u64)ramdisk_size >> 32; > + if (!noinitrd()) { > + /* > + * The initrd loaded from the Linux initrd vendor device > + * path should take precedence, as we don't want the > + * [unverified] command line to override the initrd > + * supplied by the [potentially verified] firmware. > + */ > + status = efi_load_initrd_devpath(&ramdisk_addr, &ramdisk_size, > + above4g ? ULONG_MAX > + : hdr->initrd_addr_max); > + if (status == EFI_NOT_FOUND) > + status = efi_load_initrd(image, hdr->initrd_addr_max, > + above4g ? ULONG_MAX > + : hdr->initrd_addr_max, > + &ramdisk_addr, &ramdisk_size); > + if (status != EFI_SUCCESS) > + goto fail2; > + hdr->ramdisk_image = ramdisk_addr & 0xffffffff; > + hdr->ramdisk_size = ramdisk_size & 0xffffffff; > + boot_params->ext_ramdisk_image = (u64)ramdisk_addr >> 32; > + boot_params->ext_ramdisk_size = (u64)ramdisk_size >> 32; > + } > > efi_stub_entry(handle, sys_table, boot_params); > /* not reached */ > @@ -743,7 +745,8 @@ struct boot_params *efi_main(efi_handle_t handle, > ((u64)boot_params->ext_cmd_line_ptr << 32)); > efi_parse_options((char *)cmdline_paddr); > > - if (!hdr->ramdisk_size && !boot_params->ext_ramdisk_size) { > + if (!hdr->ramdisk_size && !boot_params->ext_ramdisk_size && > + !noinitrd()) { > unsigned long max = hdr->initrd_addr_max; > unsigned long addr, size; > >
On Thu, 6 Feb 2020 at 18:33, Heinrich Schuchardt <xypron.glpk@gmx.de> wrote: > > On 2/6/20 3:03 PM, Ard Biesheuvel wrote: > > One of the advantages of using what basically amounts to a callback > > interface into the bootloader for loading the initrd is that it provides > > a natural place for the bootloader or firmware to measure the initrd > > contents while they are being passed to the kernel. > > > > Unfortunately, this is not a guarantee that the initrd will in fact be > > loaded and its /init invoked by the kernel, since the command line may > > contain the 'noinitrd' option, in which case the initrd is ignored, but > > this will not be reflected in the PCR that covers the initrd measurement. > > Does PCR here refer to the TPM Platform Configuration Register? > Yes.
On Thu, Feb 06, 2020 at 02:03:52PM +0000, Ard Biesheuvel wrote: > One of the advantages of using what basically amounts to a callback > interface into the bootloader for loading the initrd is that it provides > a natural place for the bootloader or firmware to measure the initrd > contents while they are being passed to the kernel. > > Unfortunately, this is not a guarantee that the initrd will in fact be > loaded and its /init invoked by the kernel, since the command line may > contain the 'noinitrd' option, in which case the initrd is ignored, but > this will not be reflected in the PCR that covers the initrd measurement. > > This could be addressed by measuring the command line as well, and > including that PCR in the attestation policy, but this locks down the > command line completely, which may be too restrictive. In practice I think we need to be measuring the command line anyway. In current existing deployments, we measure kernel and initramfs into PCR9, and measure the kernel command line into PCR8 (both are reserved in the TIS for OS use). This allows users farther down the stack to choose whether which things they seal against, based on their requirements. > So let's take the noinitrd argument into account in the stub, too. This > forces the PCR that covers the initrd to assume a different value when > noinitrd is passed, allowing an attestation policy to disregard the > command line if there is no need to take its measurement into account > for other reasons. I think we also need to log a capping EV_SEPARATOR event with an log entry that says it's for noinitrd into PCR9, in order to prevent any scenarios where an attacker prevents the normal initramfs from loading, and then replays the events from a prior log in order to unseal secrets.
diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c index 1db943c1ba2b..5e8f16cf016e 100644 --- a/drivers/firmware/efi/libstub/arm-stub.c +++ b/drivers/firmware/efi/libstub/arm-stub.c @@ -256,18 +256,21 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg, if (!fdt_addr) pr_efi("Generating empty DTB\n"); - max_addr = efi_get_max_initrd_addr(dram_base, *image_addr); - status = efi_load_initrd_devpath(&initrd_addr, &initrd_size, max_addr); - if (status == EFI_SUCCESS) - pr_efi("Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path\n"); - else if (status == EFI_NOT_FOUND) { - status = efi_load_initrd(image, ULONG_MAX, max_addr, - &initrd_addr, &initrd_size); + if (!noinitrd()) { + max_addr = efi_get_max_initrd_addr(dram_base, *image_addr); + status = efi_load_initrd_devpath(&initrd_addr, &initrd_size, + max_addr); if (status == EFI_SUCCESS) - pr_efi("Loaded initrd from command line option\n"); + pr_efi("Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path\n"); + else if (status == EFI_NOT_FOUND) { + status = efi_load_initrd(image, ULONG_MAX, max_addr, + &initrd_addr, &initrd_size); + if (status == EFI_SUCCESS) + pr_efi("Loaded initrd from command line option\n"); + } + if (status != EFI_SUCCESS) + pr_efi_err("Failed to load initrd!\n"); } - if (status != EFI_SUCCESS) - pr_efi_err("Failed to load initrd!\n"); efi_random_get_seed(); diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c index eaf45ea749b3..367575fb8424 100644 --- a/drivers/firmware/efi/libstub/efi-stub-helper.c +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c @@ -11,6 +11,7 @@ static bool __efistub_global efi_nochunk; static bool __efistub_global efi_nokaslr; +static bool __efistub_global efi_noinitrd; static bool __efistub_global efi_quiet; static bool __efistub_global efi_novamap; static bool __efistub_global efi_nosoftreserve; @@ -25,6 +26,10 @@ bool __pure nokaslr(void) { return efi_nokaslr; } +bool __pure noinitrd(void) +{ + return efi_noinitrd; +} bool __pure is_quiet(void) { return efi_quiet; @@ -71,6 +76,10 @@ efi_status_t efi_parse_options(char const *cmdline) if (str == cmdline || (str && str > cmdline && *(str - 1) == ' ')) efi_nokaslr = true; + str = strstr(cmdline, "noinitrd"); + if (str == cmdline || (str && str > cmdline && *(str - 1) == ' ')) + efi_noinitrd = true; + str = strstr(cmdline, "quiet"); if (str == cmdline || (str && str > cmdline && *(str - 1) == ' ')) efi_quiet = true; diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h index fbf9f9442eed..29a5d0e9554a 100644 --- a/drivers/firmware/efi/libstub/efistub.h +++ b/drivers/firmware/efi/libstub/efistub.h @@ -44,6 +44,7 @@ extern bool __pure nochunk(void); extern bool __pure nokaslr(void); +extern bool __pure noinitrd(void); extern bool __pure is_quiet(void); extern bool __pure novamap(void); diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c index 7f38f95676dd..9d86c0949b3c 100644 --- a/drivers/firmware/efi/libstub/x86-stub.c +++ b/drivers/firmware/efi/libstub/x86-stub.c @@ -419,26 +419,28 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle, if (status != EFI_SUCCESS) goto fail2; - /* - * The initrd loaded from the Linux initrd vendor device - * path should take precedence, as we don't want the - * [unverified] command line to override the initrd - * supplied by the [potentially verified] firmware. - */ - status = efi_load_initrd_devpath(&ramdisk_addr, &ramdisk_size, - above4g ? ULONG_MAX - : hdr->initrd_addr_max); - if (status == EFI_NOT_FOUND) - status = efi_load_initrd(image, hdr->initrd_addr_max, - above4g ? ULONG_MAX - : hdr->initrd_addr_max, - &ramdisk_addr, &ramdisk_size); - if (status != EFI_SUCCESS) - goto fail2; - hdr->ramdisk_image = ramdisk_addr & 0xffffffff; - hdr->ramdisk_size = ramdisk_size & 0xffffffff; - boot_params->ext_ramdisk_image = (u64)ramdisk_addr >> 32; - boot_params->ext_ramdisk_size = (u64)ramdisk_size >> 32; + if (!noinitrd()) { + /* + * The initrd loaded from the Linux initrd vendor device + * path should take precedence, as we don't want the + * [unverified] command line to override the initrd + * supplied by the [potentially verified] firmware. + */ + status = efi_load_initrd_devpath(&ramdisk_addr, &ramdisk_size, + above4g ? ULONG_MAX + : hdr->initrd_addr_max); + if (status == EFI_NOT_FOUND) + status = efi_load_initrd(image, hdr->initrd_addr_max, + above4g ? ULONG_MAX + : hdr->initrd_addr_max, + &ramdisk_addr, &ramdisk_size); + if (status != EFI_SUCCESS) + goto fail2; + hdr->ramdisk_image = ramdisk_addr & 0xffffffff; + hdr->ramdisk_size = ramdisk_size & 0xffffffff; + boot_params->ext_ramdisk_image = (u64)ramdisk_addr >> 32; + boot_params->ext_ramdisk_size = (u64)ramdisk_size >> 32; + } efi_stub_entry(handle, sys_table, boot_params); /* not reached */ @@ -743,7 +745,8 @@ struct boot_params *efi_main(efi_handle_t handle, ((u64)boot_params->ext_cmd_line_ptr << 32)); efi_parse_options((char *)cmdline_paddr); - if (!hdr->ramdisk_size && !boot_params->ext_ramdisk_size) { + if (!hdr->ramdisk_size && !boot_params->ext_ramdisk_size && + !noinitrd()) { unsigned long max = hdr->initrd_addr_max; unsigned long addr, size;
One of the advantages of using what basically amounts to a callback interface into the bootloader for loading the initrd is that it provides a natural place for the bootloader or firmware to measure the initrd contents while they are being passed to the kernel. Unfortunately, this is not a guarantee that the initrd will in fact be loaded and its /init invoked by the kernel, since the command line may contain the 'noinitrd' option, in which case the initrd is ignored, but this will not be reflected in the PCR that covers the initrd measurement. This could be addressed by measuring the command line as well, and including that PCR in the attestation policy, but this locks down the command line completely, which may be too restrictive. So let's take the noinitrd argument into account in the stub, too. This forces the PCR that covers the initrd to assume a different value when noinitrd is passed, allowing an attestation policy to disregard the command line if there is no need to take its measurement into account for other reasons. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> --- drivers/firmware/efi/libstub/arm-stub.c | 23 +++++----- drivers/firmware/efi/libstub/efi-stub-helper.c | 9 ++++ drivers/firmware/efi/libstub/efistub.h | 1 + drivers/firmware/efi/libstub/x86-stub.c | 45 +++++++++++--------- 4 files changed, 47 insertions(+), 31 deletions(-)