RE: [RFC PATCH v7 14/16] scripts: add boot policy generation program

Roberto Sassu
2021-11-03T16:53:46Z

> From: Roberto Sassu [mailto:roberto.sassu@huawei.com]
> Sent: Wednesday, November 3, 2021 5:43 PM
> > From: deven.desai@linux.microsoft.com
> > [mailto:deven.desai@linux.microsoft.com]
> > From: Deven Bowers <deven.desai@linux.microsoft.com>
> >
> > Enables an IPE policy to be enforced from kernel start, enabling access
> > control based on trust from kernel startup. This is accomplished by
> > transforming an IPE policy indicated by CONFIG_IPE_BOOT_POLICY into a
> > c-string literal that is parsed at kernel startup as an unsigned policy.
> >
> > Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>
> > ---
> >
> > Relevant changes since v6:
> > * Move patch 01/12 to [14/16] of the series
> >
> > ---
> > MAINTAINERS | 1 +
> > scripts/Makefile | 1 +
> > scripts/ipe/Makefile | 2 +
> > scripts/ipe/polgen/.gitignore | 1 +
> > scripts/ipe/polgen/Makefile | 6 ++
> > scripts/ipe/polgen/polgen.c | 145 ++++++++++++++++++++++++++++++++++
> > security/ipe/.gitignore | 1 +
> > security/ipe/Kconfig | 10 +++
> > security/ipe/Makefile | 13 +++
> > security/ipe/ctx.c | 18 +++++
> > 10 files changed, 198 insertions(+)
> > create mode 100644 scripts/ipe/Makefile
> > create mode 100644 scripts/ipe/polgen/.gitignore
> > create mode 100644 scripts/ipe/polgen/Makefile
> > create mode 100644 scripts/ipe/polgen/polgen.c
> > create mode 100644 security/ipe/.gitignore
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index f1e76f791d47..a84ca781199b 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -9283,6 +9283,7 @@ INTEGRITY POLICY ENFORCEMENT (IPE)
> > M: Deven Bowers <deven.desai@linux.microsoft.com>
> > M: Fan Wu <wufan@linux.microsoft.com>
> > S: Supported
> > +F: scripts/ipe/
> > F: security/ipe/
> >
> > INTEL 810/815 FRAMEBUFFER DRIVER
> > diff --git a/scripts/Makefile b/scripts/Makefile
> > index 9adb6d247818..a31da6d57a36 100644
> > --- a/scripts/Makefile
> > +++ b/scripts/Makefile
> > @@ -41,6 +41,7 @@ targets += module.lds
> > subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
> > subdir-$(CONFIG_MODVERSIONS) += genksyms
> > subdir-$(CONFIG_SECURITY_SELINUX) += selinux
> > +subdir-$(CONFIG_SECURITY_IPE) += ipe
> >
> > # Let clean descend into subdirs
> > subdir- += basic dtc gdb kconfig mod
> > diff --git a/scripts/ipe/Makefile b/scripts/ipe/Makefile
> > new file mode 100644
> > index 000000000000..e87553fbb8d6
> > --- /dev/null
> > +++ b/scripts/ipe/Makefile
> > @@ -0,0 +1,2 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +subdir-y := polgen
> > diff --git a/scripts/ipe/polgen/.gitignore b/scripts/ipe/polgen/.gitignore
> > new file mode 100644
> > index 000000000000..80f32f25d200
> > --- /dev/null
> > +++ b/scripts/ipe/polgen/.gitignore
> > @@ -0,0 +1 @@
> > +polgen
> > diff --git a/scripts/ipe/polgen/Makefile b/scripts/ipe/polgen/Makefile
> > new file mode 100644
> > index 000000000000..066060c22b4a
> > --- /dev/null
> > +++ b/scripts/ipe/polgen/Makefile
> > @@ -0,0 +1,6 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +hostprogs-always-y := polgen
> > +HOST_EXTRACFLAGS += \
> > + -I$(srctree)/include \
> > + -I$(srctree)/include/uapi \
> > +
> > diff --git a/scripts/ipe/polgen/polgen.c b/scripts/ipe/polgen/polgen.c
> > new file mode 100644
> > index 000000000000..73cf13e743f7
> > --- /dev/null
> > +++ b/scripts/ipe/polgen/polgen.c
> > @@ -0,0 +1,145 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) Microsoft Corporation. All rights reserved.
> > + */
> > +
> > +#include <stdlib.h>
> > +#include <stddef.h>
> > +#include <stdio.h>
> > +#include <unistd.h>
> > +#include <errno.h>
> > +
> > +static void usage(const char *const name)
> > +{
> > + printf("Usage: %s OutputFile (PolicyFile)\n", name);
> > + exit(EINVAL);
> > +}
> > +
> > +static int policy_to_buffer(const char *pathname, char **buffer, size_t *size)
> > +{
> > + int rc = 0;
> > + FILE *fd;
> > + char *lbuf;
> > + size_t fsize;
> > + size_t read;
> > +
> > + fd = fopen(pathname, "r");
> > + if (!fd) {
> > + rc = errno;
> > + goto out;
> > + }
> > +
> > + fseek(fd, 0, SEEK_END);
> > + fsize = ftell(fd);
> > + rewind(fd);
> > +
> > + lbuf = malloc(fsize);
> > + if (!lbuf) {
> > + rc = ENOMEM;
> > + goto out_close;
> > + }
> > +
> > + read = fread((void *)lbuf, sizeof(*lbuf), fsize, fd);
> > + if (read != fsize) {
> > + rc = -1;
> > + goto out_free;
> > + }
> > +
> > + *buffer = lbuf;
> > + *size = fsize;
> > + fclose(fd);
> > +
> > + return rc;
> > +
> > +out_free:
> > + free(lbuf);
> > +out_close:
> > + fclose(fd);
> > +out:
> > + return rc;
> > +}
> > +
> > +static int write_boot_policy(const char *pathname, const char *buf, size_t
> size)
> > +{
> > + int rc = 0;
> > + FILE *fd;
> > + size_t i;
> > +
> > + fd = fopen(pathname, "w");
> > + if (!fd) {
> > + rc = errno;
> > + goto err;
> > + }
> > +
> > + fprintf(fd, "/* This file is automatically generated.");
> > + fprintf(fd, " Do not edit. */\n");
> > + fprintf(fd, "#include <stddef.h>\n");
> > + fprintf(fd, "\nextern const char *const ipe_boot_policy;\n\n");
> > + fprintf(fd, "const char *const ipe_boot_policy =\n");
> > +
> > + if (!buf || size == 0) {
> > + fprintf(fd, "\tNULL;\n");
> > + fclose(fd);
> > + return 0;
> > + }
> > +
> > + fprintf(fd, "\t\"");
> > +
> > + for (i = 0; i < size; ++i) {
> > + switch (buf[i]) {
> > + case '"':
> > + fprintf(fd, "\\\"");
> > + break;
> > + case '\'':
> > + fprintf(fd, "'");
> > + break;
> > + case '\n':
> > + fprintf(fd, "\\n\"\n\t\"");
> > + break;
> > + case '\\':
> > + fprintf(fd, "\\\\");
> > + break;
> > + case '\t':
> > + fprintf(fd, "\\t");
> > + break;
> > + case '\?':
> > + fprintf(fd, "\\?");
> > + break;
> > + default:
> > + fprintf(fd, "%c", buf[i]);
> > + }
> > + }
> > + fprintf(fd, "\";\n");
> > + fclose(fd);
> > +
> > + return 0;
> > +
> > +err:
> > + if (fd)
> > + fclose(fd);
> > + return rc;
> > +}
> > +
> > +int main(int argc, const char *const argv[])
> > +{
> > + int rc = 0;
> > + size_t len = 0;
> > + char *policy = NULL;
> > +
> > + if (argc < 2)
> > + usage(argv[0]);
> > +
> > + if (argc > 2) {
> > + rc = policy_to_buffer(argv[2], &policy, &len);
> > + if (rc != 0)
> > + goto cleanup;
> > + }
> > +
> > + rc = write_boot_policy(argv[1], policy, len);
> > +cleanup:
> > + if (policy)
> > + free(policy);
> > + if (rc != 0)
> > + perror("An error occurred during policy conversion: ");
> > + return rc;
> > +}
> > diff --git a/security/ipe/.gitignore b/security/ipe/.gitignore
> > new file mode 100644
> > index 000000000000..eca22ad5ed22
> > --- /dev/null
> > +++ b/security/ipe/.gitignore
> > @@ -0,0 +1 @@
> > +boot-policy.c
> > \ No newline at end of file
> > diff --git a/security/ipe/Kconfig b/security/ipe/Kconfig
> > index fcf82a8152ec..39df680b67a2 100644
> > --- a/security/ipe/Kconfig
> > +++ b/security/ipe/Kconfig
> > @@ -20,6 +20,16 @@ menuconfig SECURITY_IPE
> >
> > if SECURITY_IPE
> >
> > +config IPE_BOOT_POLICY
> > + string "Integrity policy to apply on system startup"
> > + help
> > + This option specifies a filepath to a IPE policy that is compiled
> > + into the kernel. This policy will be enforced until a policy update
> > + is deployed via the $securityfs/ipe/policies/$policy_name/active
> > + interface.
> > +
> > + If unsure, leave blank.
> > +
> > choice
> > prompt "Hash algorithm used in auditing policies"
> > default IPE_AUDIT_HASH_SHA1
> > diff --git a/security/ipe/Makefile b/security/ipe/Makefile
> > index 1e7b2d7fcd9e..89fec670f954 100644
> > --- a/security/ipe/Makefile
> > +++ b/security/ipe/Makefile
> > @@ -7,7 +7,18 @@
> >
> > ccflags-y := -I$(srctree)/security/ipe/modules
> >
> > +quiet_cmd_polgen = IPE_POL $(2)
> > + cmd_polgen = scripts/ipe/polgen/polgen security/ipe/boot-policy.c $(2)
> > +
> > +$(eval $(call config_filename,IPE_BOOT_POLICY))
> > +
> > +targets += boot-policy.c
> > +
> > +$(obj)/boot-policy.c: scripts/ipe/polgen/polgen
> > $(IPE_BOOT_POLICY_FILENAME) FORCE
> > + $(call if_changed,polgen,$(IPE_BOOT_POLICY_FILENAME))
> > +
> > obj-$(CONFIG_SECURITY_IPE) += \
> > + boot-policy.o \
> > ctx.o \
> > eval.o \
> > fs.o \
> > @@ -21,3 +32,5 @@ obj-$(CONFIG_SECURITY_IPE) += \
> > policyfs.o \
> >
> > obj-$(CONFIG_AUDIT) += audit.o
> > +
> > +clean-files := boot-policy.c \
> > diff --git a/security/ipe/ctx.c b/security/ipe/ctx.c
> > index fc9b8e467bc9..879acf4ceac5 100644
> > --- a/security/ipe/ctx.c
> > +++ b/security/ipe/ctx.c
> > @@ -15,6 +15,7 @@
> > #include <linux/spinlock.h>
> > #include <linux/moduleparam.h>
> >
> > +extern const char *const ipe_boot_policy;
> > static bool success_audit;
> > static bool enforce = true;
> >
> > @@ -329,6 +330,7 @@ void ipe_put_ctx(struct ipe_context *ctx)
> > int __init ipe_init_ctx(void)
> > {
> > int rc = 0;
> > + struct ipe_policy *p = NULL;
> > struct ipe_context *lns = NULL;
> >
> > lns = create_ctx();
> > @@ -342,10 +344,26 @@ int __init ipe_init_ctx(void)
> > WRITE_ONCE(lns->enforce, enforce);
> > spin_unlock(&lns->lock);
> >
> > + if (ipe_boot_policy) {
> > + p = ipe_new_policy(ipe_boot_policy, strlen(ipe_boot_policy),
> > + NULL, 0);
> > + if (IS_ERR(p)) {
> > + rc = PTR_ERR(lns);
>
> This should be:
>
> rc = PTR_ERR(p);
>
> > + goto err;
> > + }
> > +
> > + ipe_add_policy(lns, p);
> > + rc = ipe_set_active_pol(p);
> > + if (!rc)
>
> Here you need to set a non-zero value, so that ipe_init()
> does not enable the LSM.

Actually you probably should just check that rc is not zero
and goto err.

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Zhong Ronghua

> I would set to 1 a new global variable, like ipe_lsm_enabled,
> in ipe_init() just before security_add_hooks().
>
> Then, I would add a check of this variable in ipe_init_securityfs()
> to avoid the kernel panic.
>
> Roberto
>
> HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
> Managing Director: Li Peng, Zhong Ronghua
>
> > + goto err;
> > + }
> > +
> > rcu_assign_pointer(*ipe_tsk_ctx(current), lns);
> > + ipe_put_policy(p);
> >
> > return 0;
> > err:
> > + ipe_put_policy(p);
> > ipe_put_ctx(lns);
> > return rc;
> > }
> > --
> > 2.33.0