[PATCH v3 3/4] efi_loader: add an EFI variable with the file contents
Ilias Apalodimas
ilias.apalodimas at linaro.org
Thu Apr 18 17:36:55 CEST 2024
Hi Mark,
On Thu, 18 Apr 2024 at 18:15, Mark Kettenis <mark.kettenis at xs4all.nl> wrote:
>
> > From: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> > Date: Thu, 18 Apr 2024 15:54:52 +0300
>
> Hi Illias,
>
> >
> > Previous patches enabled SetVariableRT using a RAM backend.
> > Although EBBR [0] defines a variable format we can teach userspace tools
> > and write the altered variables, it's better if we skip the ABI
> > requirements completely.
> >
> > So let's add a new variable, in its own namespace called "VarToFile"
> > which contains a binary dump of the updated RT, BS and, NV variables
> > and will be updated when GetVariable is called.
> >
> > Some adjustments are needed to do that.
> > Currently we discard BS-only variables in EBS(). We need to preserve
> > those on the RAM backend that exposes the variables. Since BS-only
> > variables can't appear at runtime we need to move the memory masking
> > checks from efi_var_collect() to efi_get_next_variable_name_mem()/
> > efi_get_variable_mem() and do the filtering at runtime.
> >
> > We also need an efi_var_collect() variant available at runtime, in order
> > to construct the "VarToFile" buffer on the fly.
> >
> > All users and applications (for linux) have to do when updating a variable
> > is dd that variable in the file described by "RTStorageVolatile".
>
> I simehow missed your reply to the issue I raised with picking the
> right ESP to write variables back to.
No worries, I did send v3 quickly myself...
> I'm not convinced that the ESP
> that was used to install Linux on is necessarily th right one. In
> particular, consider a system with multiple disks, say eMMC and an
> NVMe disk. Suppose U-Boot is installed on eMMC and picks the ESP on
> that disk to store the EFI variables.
And who creates ESP on the eMMC? I assume you have one OS installed in
the eMMC and another one in the nvme?
> Now I install Linux on the NVMe
> disk, which creates an ESP to store its bootloader. With your
> proposed changes, Linux will probably end up writing the variables to
> the ESP on the NVMe. Now you reboot and U-Boot still reads the EFI
> variables from eMMC and you've lost any changes...
I understand the problem, but my concern is that using a DP just
delegates the problem -- it doesn't solve it.
To use the 'correct' partition, U-Boot has to *decide* which ESP is
going to be used and inject it in RTVolatileStorage.
But if U-Boot decides about the 'correct' ESP the relative path would
work as well. So what's needed here is a mechanism to correlate the
booted OS with the ESP it will use and force the variable loading from
that file. Am I missing anything?
/Ilias
>
> > Linux efivarfs uses a first 4 bytes of the output to represent attributes
> > in little-endian format. So, storing variables works like this:
> >
> > $~ efibootmgr -n 0001
> > $~ dd if=/sys/firmware/efi/efivars/VarToFile-b2ac5fc9-92b7-4acd-aeac-11e818c3130c of=/boot/efi/ubootefi.var skip=4 bs=1
> >
> > [0] https://arm-software.github.io/ebbr/index.html#document-chapter5-variable-storage
> >
> > Suggested-by: Ard Biesheuvel <ardb at kernel.org> # dumping all variables to a variable
> > Co-developed-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com> # contributed on efi_var_collect_mem()
> > Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> > Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> > ---
> > include/efi_variable.h | 16 +++-
> > lib/charset.c | 2 +-
> > lib/efi_loader/efi_runtime.c | 25 +++++
> > lib/efi_loader/efi_var_common.c | 6 +-
> > lib/efi_loader/efi_var_mem.c | 151 +++++++++++++++++++-----------
> > lib/efi_loader/efi_variable.c | 6 +-
> > lib/efi_loader/efi_variable_tee.c | 5 -
> > 7 files changed, 146 insertions(+), 65 deletions(-)
> >
> > diff --git a/include/efi_variable.h b/include/efi_variable.h
> > index 42a2b7c52bef..223bb9a4a5bd 100644
> > --- a/include/efi_variable.h
> > +++ b/include/efi_variable.h
> > @@ -271,13 +271,16 @@ const efi_guid_t *efi_auth_var_get_guid(const u16 *name);
> > *
> > * @variable_name_size: size of variable_name buffer in bytes
> > * @variable_name: name of uefi variable's name in u16
> > + * @mask: bitmask with required attributes of variables to be collected.
> > + * variables are only collected if all of the required
> > + * attributes match. Use 0 to skip matching
> > * @vendor: vendor's guid
> > *
> > * Return: status code
> > */
> > efi_status_t __efi_runtime
> > efi_get_next_variable_name_mem(efi_uintn_t *variable_name_size, u16 *variable_name,
> > - efi_guid_t *vendor);
> > + efi_guid_t *vendor, u32 mask);
> > /**
> > * efi_get_variable_mem() - Runtime common code across efi variable
> > * implementations for GetVariable() from
> > @@ -289,12 +292,15 @@ efi_get_next_variable_name_mem(efi_uintn_t *variable_name_size, u16 *variable_na
> > * @data_size: size of the buffer to which the variable value is copied
> > * @data: buffer to which the variable value is copied
> > * @timep: authentication time (seconds since start of epoch)
> > + * @mask: bitmask with required attributes of variables to be collected.
> > + * variables are only collected if all of the required
> > + * attributes match. Use 0 to skip matching
> > * Return: status code
> > */
> > efi_status_t __efi_runtime
> > efi_get_variable_mem(const u16 *variable_name, const efi_guid_t *vendor,
> > u32 *attributes, efi_uintn_t *data_size, void *data,
> > - u64 *timep);
> > + u64 *timep, u32 mask);
> >
> > /**
> > * efi_get_variable_runtime() - runtime implementation of GetVariable()
> > @@ -334,4 +340,10 @@ efi_get_next_variable_name_runtime(efi_uintn_t *variable_name_size,
> > */
> > void efi_var_buf_update(struct efi_var_file *var_buf);
> >
> > +efi_status_t __efi_runtime efi_var_collect_mem(struct efi_var_file *buf,
> > + efi_uintn_t *lenp,
> > + u32 check_attr_mask);
> > +
> > +u32 efi_var_entry_len(struct efi_var_entry *var);
> > +
> > #endif
> > diff --git a/lib/charset.c b/lib/charset.c
> > index df4f04074852..182c92a50c48 100644
> > --- a/lib/charset.c
> > +++ b/lib/charset.c
> > @@ -387,7 +387,7 @@ int u16_strcasecmp(const u16 *s1, const u16 *s2)
> > * > 0 if the first different u16 in s1 is greater than the
> > * corresponding u16 in s2
> > */
> > -int u16_strncmp(const u16 *s1, const u16 *s2, size_t n)
> > +int __efi_runtime u16_strncmp(const u16 *s1, const u16 *s2, size_t n)
> > {
> > int ret = 0;
> >
> > diff --git a/lib/efi_loader/efi_runtime.c b/lib/efi_loader/efi_runtime.c
> > index c8f7a88ba8db..73831c527e00 100644
> > --- a/lib/efi_loader/efi_runtime.c
> > +++ b/lib/efi_loader/efi_runtime.c
> > @@ -130,6 +130,8 @@ efi_status_t efi_init_runtime_supported(void)
> > EFI_RT_SUPPORTED_CONVERT_POINTER;
> >
> > if (IS_ENABLED(CONFIG_EFI_RT_VOLATILE_STORE)) {
> > + u8 s = 0;
> > +
> > ret = efi_set_variable_int(u"RTStorageVolatile",
> > &efi_guid_efi_rt_var_file,
> > EFI_VARIABLE_BOOTSERVICE_ACCESS |
> > @@ -141,6 +143,29 @@ efi_status_t efi_init_runtime_supported(void)
> > log_err("Failed to set RTStorageVolatile\n");
> > return ret;
> > }
> > + /*
> > + * This variable needs to be visible so users can read it,
> > + * but the real contents are going to be filled during
> > + * GetVariable
> > + */
> > + ret = efi_set_variable_int(u"VarToFile",
> > + &efi_guid_efi_rt_var_file,
> > + EFI_VARIABLE_BOOTSERVICE_ACCESS |
> > + EFI_VARIABLE_RUNTIME_ACCESS |
> > + EFI_VARIABLE_READ_ONLY,
> > + sizeof(s),
> > + &s, false);
> > + if (ret != EFI_SUCCESS) {
> > + log_err("Failed to set VarToFile\n");
> > + efi_set_variable_int(u"RTStorageVolatile",
> > + &efi_guid_efi_rt_var_file,
> > + EFI_VARIABLE_BOOTSERVICE_ACCESS |
> > + EFI_VARIABLE_RUNTIME_ACCESS |
> > + EFI_VARIABLE_READ_ONLY,
> > + 0, NULL, false);
> > +
> > + return ret;
> > + }
> > rt_table->runtime_services_supported |= EFI_RT_SUPPORTED_SET_VARIABLE;
> > }
> >
> > diff --git a/lib/efi_loader/efi_var_common.c b/lib/efi_loader/efi_var_common.c
> > index aa8feffd3ec1..7862f2d6ce8a 100644
> > --- a/lib/efi_loader/efi_var_common.c
> > +++ b/lib/efi_loader/efi_var_common.c
> > @@ -182,7 +182,8 @@ efi_get_variable_runtime(u16 *variable_name, const efi_guid_t *guid,
> > {
> > efi_status_t ret;
> >
> > - ret = efi_get_variable_mem(variable_name, guid, attributes, data_size, data, NULL);
> > + ret = efi_get_variable_mem(variable_name, guid, attributes, data_size,
> > + data, NULL, EFI_VARIABLE_RUNTIME_ACCESS);
> >
> > /* Remove EFI_VARIABLE_READ_ONLY flag */
> > if (attributes)
> > @@ -195,7 +196,8 @@ efi_status_t __efi_runtime EFIAPI
> > efi_get_next_variable_name_runtime(efi_uintn_t *variable_name_size,
> > u16 *variable_name, efi_guid_t *guid)
> > {
> > - return efi_get_next_variable_name_mem(variable_name_size, variable_name, guid);
> > + return efi_get_next_variable_name_mem(variable_name_size, variable_name,
> > + guid, EFI_VARIABLE_RUNTIME_ACCESS);
> > }
> >
> > /**
> > diff --git a/lib/efi_loader/efi_var_mem.c b/lib/efi_loader/efi_var_mem.c
> > index 6c21cec5d457..940ab6638823 100644
> > --- a/lib/efi_loader/efi_var_mem.c
> > +++ b/lib/efi_loader/efi_var_mem.c
> > @@ -61,6 +61,23 @@ efi_var_mem_compare(struct efi_var_entry *var, const efi_guid_t *guid,
> > return match;
> > }
> >
> > +/**
> > + * efi_var_entry_len() - Get the entry len including headers & name
> > + *
> > + * @var: pointer to variable start
> > + *
> > + * Return: 8-byte aligned variable entry length
> > + */
> > +
> > +u32 __efi_runtime efi_var_entry_len(struct efi_var_entry *var)
> > +{
> > + if (!var)
> > + return 0;
> > +
> > + return ALIGN((sizeof(u16) * (u16_strlen(var->name) + 1)) +
> > + var->length + sizeof(*var), 8);
> > +}
> > +
> > struct efi_var_entry __efi_runtime
> > *efi_var_mem_find(const efi_guid_t *guid, const u16 *name,
> > struct efi_var_entry **next)
> > @@ -184,53 +201,6 @@ u64 __efi_runtime efi_var_mem_free(void)
> > sizeof(struct efi_var_entry);
> > }
> >
> > -/**
> > - * efi_var_mem_bs_del() - delete boot service only variables
> > - */
> > -static void efi_var_mem_bs_del(void)
> > -{
> > - struct efi_var_entry *var = efi_var_buf->var;
> > -
> > - for (;;) {
> > - struct efi_var_entry *last;
> > -
> > - last = (struct efi_var_entry *)
> > - ((uintptr_t)efi_var_buf + efi_var_buf->length);
> > - if (var >= last)
> > - break;
> > - if (var->attr & EFI_VARIABLE_RUNTIME_ACCESS) {
> > - u16 *data;
> > -
> > - /* skip variable */
> > - for (data = var->name; *data; ++data)
> > - ;
> > - ++data;
> > - var = (struct efi_var_entry *)
> > - ALIGN((uintptr_t)data + var->length, 8);
> > - } else {
> > - /* delete variable */
> > - efi_var_mem_del(var);
> > - }
> > - }
> > -}
> > -
> > -/**
> > - * efi_var_mem_notify_exit_boot_services() - ExitBootService callback
> > - *
> > - * @event: callback event
> > - * @context: callback context
> > - */
> > -static void EFIAPI
> > -efi_var_mem_notify_exit_boot_services(struct efi_event *event, void *context)
> > -{
> > - EFI_ENTRY("%p, %p", event, context);
> > -
> > - /* Delete boot service only variables */
> > - efi_var_mem_bs_del();
> > -
> > - EFI_EXIT(EFI_SUCCESS);
> > -}
> > -
> > /**
> > * efi_var_mem_notify_exit_boot_services() - SetVirtualMemoryMap callback
> > *
> > @@ -261,11 +231,7 @@ efi_status_t efi_var_mem_init(void)
> > efi_var_buf->magic = EFI_VAR_FILE_MAGIC;
> > efi_var_buf->length = (uintptr_t)efi_var_buf->var -
> > (uintptr_t)efi_var_buf;
> > - /* crc32 for 0 bytes = 0 */
> >
> > - ret = efi_create_event(EVT_SIGNAL_EXIT_BOOT_SERVICES, TPL_CALLBACK,
> > - efi_var_mem_notify_exit_boot_services, NULL,
> > - NULL, &event);
> > if (ret != EFI_SUCCESS)
> > return ret;
> > ret = efi_create_event(EVT_SIGNAL_VIRTUAL_ADDRESS_CHANGE, TPL_CALLBACK,
> > @@ -276,10 +242,71 @@ efi_status_t efi_var_mem_init(void)
> > return ret;
> > }
> >
> > +/**
> > + * efi_var_collect_mem() - Copy EFI variables matching attributes mask from
> > + * efi_var_buf
> > + *
> > + * @buf: buffer containing variable collection
> > + * @lenp: buffer length
> > + * @mask: mask of matched attributes
> > + *
> > + * Return: Status code
> > + */
> > +efi_status_t __efi_runtime
> > +efi_var_collect_mem(struct efi_var_file *buf, efi_uintn_t *lenp, u32 mask)
> > +{
> > + static struct efi_var_file __efi_runtime_data hdr = {
> > + .magic = EFI_VAR_FILE_MAGIC,
> > + };
> > + struct efi_var_entry *last, *var, *var_to;
> > +
> > + hdr.length = sizeof(struct efi_var_file);
> > +
> > + var = efi_var_buf->var;
> > + last = (struct efi_var_entry *)
> > + ((uintptr_t)efi_var_buf + efi_var_buf->length);
> > + if (buf)
> > + var_to = buf->var;
> > +
> > + while (var < last) {
> > + u32 len = efi_var_entry_len(var);
> > +
> > + if ((var->attr & mask) != mask) {
> > + var = (void *)((uintptr_t)var + len);
> > + continue;
> > + }
> > +
> > + hdr.length += len;
> > +
> > + if (buf && hdr.length <= *lenp) {
> > + efi_memcpy_runtime(var_to, var, len);
> > + var_to = (void *)var_to + len;
> > + }
> > + var = (void *)var + len;
> > + }
> > +
> > + if (!buf && hdr.length <= *lenp) {
> > + *lenp = hdr.length;
> > + return EFI_INVALID_PARAMETER;
> > + }
> > +
> > + if (!buf || hdr.length > *lenp) {
> > + *lenp = hdr.length;
> > + return EFI_BUFFER_TOO_SMALL;
> > + }
> > + hdr.crc32 = crc32(0, (u8 *)buf->var,
> > + hdr.length - sizeof(struct efi_var_file));
> > +
> > + efi_memcpy_runtime(buf, &hdr, sizeof(hdr));
> > + *lenp = hdr.length;
> > +
> > + return EFI_SUCCESS;
> > +}
> > +
> > efi_status_t __efi_runtime
> > efi_get_variable_mem(const u16 *variable_name, const efi_guid_t *vendor,
> > u32 *attributes, efi_uintn_t *data_size, void *data,
> > - u64 *timep)
> > + u64 *timep, u32 mask)
> > {
> > efi_uintn_t old_size;
> > struct efi_var_entry *var;
> > @@ -291,11 +318,22 @@ efi_get_variable_mem(const u16 *variable_name, const efi_guid_t *vendor,
> > if (!var)
> > return EFI_NOT_FOUND;
> >
> > + /*
> > + * This function is used at runtime to dump EFI variables.
> > + * The memory backend we keep around has BS-only variables as
> > + * well. At runtime we filter them here
> > + */
> > + if (mask && !((var->attr & mask) == mask))
> > + return EFI_NOT_FOUND;
> > +
> > if (attributes)
> > *attributes = var->attr;
> > if (timep)
> > *timep = var->time;
> >
> > + if (!u16_strcmp(variable_name, u"VarToFile"))
> > + return efi_var_collect_mem(data, data_size, EFI_VARIABLE_NON_VOLATILE);
> > +
> > old_size = *data_size;
> > *data_size = var->length;
> > if (old_size < var->length)
> > @@ -315,7 +353,8 @@ efi_get_variable_mem(const u16 *variable_name, const efi_guid_t *vendor,
> >
> > efi_status_t __efi_runtime
> > efi_get_next_variable_name_mem(efi_uintn_t *variable_name_size,
> > - u16 *variable_name, efi_guid_t *vendor)
> > + u16 *variable_name, efi_guid_t *vendor,
> > + u32 mask)
> > {
> > struct efi_var_entry *var;
> > efi_uintn_t len, old_size;
> > @@ -324,6 +363,7 @@ efi_get_next_variable_name_mem(efi_uintn_t *variable_name_size,
> > if (!variable_name_size || !variable_name || !vendor)
> > return EFI_INVALID_PARAMETER;
> >
> > +skip:
> > len = *variable_name_size >> 1;
> > if (u16_strnlen(variable_name, len) == len)
> > return EFI_INVALID_PARAMETER;
> > @@ -347,6 +387,11 @@ efi_get_next_variable_name_mem(efi_uintn_t *variable_name_size,
> > efi_memcpy_runtime(variable_name, var->name, *variable_name_size);
> > efi_memcpy_runtime(vendor, &var->guid, sizeof(efi_guid_t));
> >
> > + if (mask && !((var->attr & mask) == mask)) {
> > + *variable_name_size = old_size;
> > + goto skip;
> > + }
> > +
> > return EFI_SUCCESS;
> > }
> >
> > diff --git a/lib/efi_loader/efi_variable.c b/lib/efi_loader/efi_variable.c
> > index 47bb79920575..0cbed53d1dbf 100644
> > --- a/lib/efi_loader/efi_variable.c
> > +++ b/lib/efi_loader/efi_variable.c
> > @@ -209,14 +209,16 @@ efi_get_variable_int(const u16 *variable_name, const efi_guid_t *vendor,
> > u32 *attributes, efi_uintn_t *data_size, void *data,
> > u64 *timep)
> > {
> > - return efi_get_variable_mem(variable_name, vendor, attributes, data_size, data, timep);
> > + return efi_get_variable_mem(variable_name, vendor, attributes, data_size,
> > + data, timep, 0);
> > }
> >
> > efi_status_t __efi_runtime
> > efi_get_next_variable_name_int(efi_uintn_t *variable_name_size,
> > u16 *variable_name, efi_guid_t *vendor)
> > {
> > - return efi_get_next_variable_name_mem(variable_name_size, variable_name, vendor);
> > + return efi_get_next_variable_name_mem(variable_name_size, variable_name,
> > + vendor, 0);
> > }
> >
> > /**
> > diff --git a/lib/efi_loader/efi_variable_tee.c b/lib/efi_loader/efi_variable_tee.c
> > index dde135fd9f81..4f1aa298da13 100644
> > --- a/lib/efi_loader/efi_variable_tee.c
> > +++ b/lib/efi_loader/efi_variable_tee.c
> > @@ -959,11 +959,6 @@ void efi_variables_boot_exit_notify(void)
> > log_err("Unable to notify the MM partition for ExitBootServices\n");
> > free(comm_buf);
> >
> > - /*
> > - * Populate the list for runtime variables.
> > - * asking EFI_VARIABLE_RUNTIME_ACCESS is redundant, since
> > - * efi_var_mem_notify_exit_boot_services will clean those, but that's fine
> > - */
> > ret = efi_var_collect(&var_buf, &len, EFI_VARIABLE_RUNTIME_ACCESS);
> > if (ret != EFI_SUCCESS)
> > log_err("Can't populate EFI variables. No runtime variables will be available\n");
> > --
> > 2.40.1
> >
> >
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