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efivarfs: Rate limit statfs() handler

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Ravi reports that statfs() may be called by unprivileged users on the
efivarfs mount point, which may result in a flood of calls to the
QueryVariableInfo() runtime service. These calls are disproportionately
costly on x86 systems where the variable store is backed by SMM, as each
SMM entry requires a rendez-vous of all the CPUs.

So rate limit the calls to QueryVariableInfo() at twice per second, and
return the most recently obtained value for calls that are elided.

Cc: <stable@vger.kernel.org>
Reported-by: Ravi Bangoria <ravi.bangoria@amd.com>
Fixes: d86ff3333c ("efivarfs: expose used and total size")
Reviewed-by: Anisse Astier <anisse@astier.eu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Ard Biesheuvel
2026-08-20 14:49:39 +03:00
parent eb01ffabeb
commit b2326338dc
1 changed files with 24 additions and 6 deletions
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fs/efivarfs/super.c
+24 -6
View File
@@ -89,12 +89,30 @@ static int efivarfs_statfs(struct dentry *dentry, struct kstatfs *buf)
/* Some UEFI firmware does not implement QueryVariableInfo() */
storage_space = remaining_space = 0;
if (efi_rt_services_supported(EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO)) {
status = efivar_query_variable_info(attr, &storage_space,
&remaining_space,
&max_variable_size);
if (status != EFI_SUCCESS && status != EFI_UNSUPPORTED)
pr_warn_ratelimited("query_variable_info() failed: 0x%lx\n",
status);
static DEFINE_RATELIMIT_STATE(_rs, 2 * HZ, 5);
static u64 storage, remaining;
static DEFINE_SPINLOCK(lock);
if (!__ratelimit(&_rs)) {
ratelimit_set_flags(&_rs, RATELIMIT_MSG_ON_RELEASE);
spin_lock(&lock);
storage_space = storage;
remaining_space = remaining;
spin_unlock(&lock);
} else {
status = efivar_query_variable_info(attr, &storage_space,
&remaining_space,
&max_variable_size);
if (status != EFI_SUCCESS && status != EFI_UNSUPPORTED)
pr_warn("query_variable_info() failed: 0x%lx\n",
status);
spin_lock(&lock);
storage = storage_space;
remaining = remaining_space;
spin_unlock(&lock);
}
}
/*