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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Wed, 29 Jul 2020 17:46:16 +1000
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Subject: [PATCH] verifiers: provide unsafe module list
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Other verifiers that implement secure boot may want to be able to
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use this list and behaviour.
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Upstream, this factors the list out of the shim_lock verifier.
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However, that hasn't hit the RHEL8.4 tree yet, so instead
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of factoring it out of that we just create it.
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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---
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grub-core/commands/verifiers.c | 46 ++++++++++++++++++++++++++++++++++++++++++
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include/grub/verify.h | 13 ++++++++++++
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2 files changed, 59 insertions(+)
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diff --git a/grub-core/commands/verifiers.c b/grub-core/commands/verifiers.c
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index 599d79b75..f64343ac9 100644
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--- a/grub-core/commands/verifiers.c
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+++ b/grub-core/commands/verifiers.c
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@@ -218,6 +218,52 @@ grub_verify_string (char *str, enum grub_verify_string_type type)
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return GRUB_ERR_NONE;
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}
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+/* List of modules which may allow for verifcation to be bypassed. */
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+static const char *const disabled_mods[] = { "iorw", "memrw", "wrmsr", NULL };
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+
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+/*
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+ * Does the module in file `io' allow for the a verifier to be bypassed?
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+ *
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+ * Returns 1 if so, otherwise 0.
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+ */
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+char
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+grub_is_dangerous_module (grub_file_t io)
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+{
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+ char *b, *e;
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+ int i;
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+
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+ /* Establish GRUB module name. */
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+ b = grub_strrchr (io->name, '/');
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+ e = grub_strrchr (io->name, '.');
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+
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+ b = b ? (b + 1) : io->name;
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+ e = e ? e : io->name + grub_strlen (io->name);
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+ e = (e > b) ? e : io->name + grub_strlen (io->name);
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+
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+ for (i = 0; disabled_mods[i]; i++)
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+ if (!grub_strncmp (b, disabled_mods[i],
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+ grub_strlen (b) - grub_strlen (e)))
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+ return 1;
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+ return 0;
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+}
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+
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+/*
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+ * Is there already an unsafe module in memory?
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+ * Returns the name if one is loaded, otherwise NULL.
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+ */
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+const char *
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+grub_dangerous_module_loaded (void)
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+{
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+ int i;
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+
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+ for (i = 0; disabled_mods[i]; i++)
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+ if (grub_dl_get (disabled_mods[i]))
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+ {
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+ return disabled_mods[i];
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+ }
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+ return NULL;
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+}
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+
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GRUB_MOD_INIT(verifiers)
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{
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grub_file_filter_register (GRUB_FILE_FILTER_VERIFY, grub_verifiers_open);
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diff --git a/include/grub/verify.h b/include/grub/verify.h
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index 79022b422..60c13e7ea 100644
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--- a/include/grub/verify.h
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+++ b/include/grub/verify.h
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@@ -76,3 +76,16 @@ grub_verifier_unregister (struct grub_file_verifier *ver)
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grub_err_t
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grub_verify_string (char *str, enum grub_verify_string_type type);
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+
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+/*
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+ * Does the module in file `io' allow for the a verifier to be bypassed?
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+ *
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+ * Returns 1 if so, otherwise 0.
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+ */
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+char grub_is_dangerous_module (grub_file_t io);
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+
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+/*
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+ * Is there already an unsafe module in memory?
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+ * Returns the name if one is loaded, otherwise NULL.
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+ */
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+const char *grub_dangerous_module_loaded (void);
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