efi: Add nonblocking option to efi_query_variable_store()

The function efi_query_variable_store() may be invoked by
efivar_entry_set_nonblocking(), which itself takes care to only
call a non-blocking version of the SetVariable() runtime
wrapper. However, efi_query_variable_store() may call the
SetVariable() wrapper directly, as well as the wrapper for
QueryVariableInfo(), both of which could deadlock in the same
way we are trying to prevent by calling
efivar_entry_set_nonblocking() in the first place.

So instead, modify efi_query_variable_store() to use the
non-blocking variants of QueryVariableInfo() (and give up rather
than free up space if the available space is below
EFI_MIN_RESERVE) if invoked with the 'nonblocking' argument set
to true.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/1454364428-494-5-git-send-email-matt@codeblueprint.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index 453504662a3316608a05647b84bafe3e8ed366ef..2326bf51978f04e0bc3da8a30375a57536ea5bca 100644 (file)
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -56,6 +56,33 @@ void efi_delete_dummy_variable(void)
                         0, NULL);
 }
 
+/*
+ * In the nonblocking case we do not attempt to perform garbage
+ * collection if we do not have enough free space. Rather, we do the
+ * bare minimum check and give up immediately if the available space
+ * is below EFI_MIN_RESERVE.
+ *
+ * This function is intended to be small and simple because it is
+ * invoked from crash handler paths.
+ */
+static efi_status_t
+query_variable_store_nonblocking(u32 attributes, unsigned long size)
+{
+       efi_status_t status;
+       u64 storage_size, remaining_size, max_size;
+
+       status = efi.query_variable_info_nonblocking(attributes, &storage_size,
+                                                    &remaining_size,
+                                                    &max_size);
+       if (status != EFI_SUCCESS)
+               return status;
+
+       if (remaining_size - size < EFI_MIN_RESERVE)
+               return EFI_OUT_OF_RESOURCES;
+
+       return EFI_SUCCESS;
+}
+
 /*
  * Some firmware implementations refuse to boot if there's insufficient space
  * in the variable store. Ensure that we never use more than a safe limit.
@@ -63,7 +90,8 @@ void efi_delete_dummy_variable(void)
  * Return EFI_SUCCESS if it is safe to write 'size' bytes to the variable
  * store.
  */
-efi_status_t efi_query_variable_store(u32 attributes, unsigned long size)
+efi_status_t efi_query_variable_store(u32 attributes, unsigned long size,
+                                     bool nonblocking)
 {
        efi_status_t status;
        u64 storage_size, remaining_size, max_size;
@@ -71,6 +99,9 @@ efi_status_t efi_query_variable_store(u32 attributes, unsigned long size)
        if (!(attributes & EFI_VARIABLE_NON_VOLATILE))
                return 0;
 
+       if (nonblocking)
+               return query_variable_store_nonblocking(attributes, size);
+
        status = efi.query_variable_info(attributes, &storage_size,
                                         &remaining_size, &max_size);
        if (status != EFI_SUCCESS)

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 70a0fb10517f94ea5b28bada280d9935f0693cc7..d2a49626a3355942f0da4c91047f16f0fbb49939 100644 (file)
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -234,7 +234,18 @@ check_var_size(u32 attributes, unsigned long size)
        if (!fops->query_variable_store)
                return EFI_UNSUPPORTED;
 
-       return fops->query_variable_store(attributes, size);
+       return fops->query_variable_store(attributes, size, false);
+}
+
+static efi_status_t
+check_var_size_nonblocking(u32 attributes, unsigned long size)
+{
+       const struct efivar_operations *fops = __efivars->ops;
+
+       if (!fops->query_variable_store)
+               return EFI_UNSUPPORTED;
+
+       return fops->query_variable_store(attributes, size, true);
 }
 
 static int efi_status_to_err(efi_status_t status)
@@ -615,7 +626,8 @@ efivar_entry_set_nonblocking(efi_char16_t *name, efi_guid_t vendor,
        if (!spin_trylock_irqsave(&__efivars->lock, flags))
                return -EBUSY;
 
-       status = check_var_size(attributes, size + ucs2_strsize(name, 1024));
+       status = check_var_size_nonblocking(attributes,
+                                           size + ucs2_strsize(name, 1024));
        if (status != EFI_SUCCESS) {
                spin_unlock_irqrestore(&__efivars->lock, flags);
                return -ENOSPC;

diff --git a/include/linux/efi.h b/include/linux/efi.h
index ad1e177ba48e236b9c906187c8baf4fd3f7bc09c..09f1559e75255b168994985ec9a92c958a2eeaf4 100644 (file)
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -525,7 +525,9 @@ typedef efi_status_t efi_query_capsule_caps_t(efi_capsule_header_t **capsules,
                                              unsigned long count,
                                              u64 *max_size,
                                              int *reset_type);
-typedef efi_status_t efi_query_variable_store_t(u32 attributes, unsigned long size);
+typedef efi_status_t efi_query_variable_store_t(u32 attributes,
+                                               unsigned long size,
+                                               bool nonblocking);
 
 void efi_native_runtime_setup(void);
 
@@ -881,13 +883,17 @@ extern void efi_enter_virtual_mode (void);        /* switch EFI to virtual mode, if pos
 #ifdef CONFIG_X86
 extern void efi_late_init(void);
 extern void efi_free_boot_services(void);
-extern efi_status_t efi_query_variable_store(u32 attributes, unsigned long size);
+extern efi_status_t efi_query_variable_store(u32 attributes,
+                                            unsigned long size,
+                                            bool nonblocking);
 extern void efi_find_mirror(void);
 #else
 static inline void efi_late_init(void) {}
 static inline void efi_free_boot_services(void) {}
 
-static inline efi_status_t efi_query_variable_store(u32 attributes, unsigned long size)
+static inline efi_status_t efi_query_variable_store(u32 attributes,
+                                                   unsigned long size,
+                                                   bool nonblocking)
 {
        return EFI_SUCCESS;
 }