[PATCH v2 0/2] powerpc/pseries: restrict error injection and DT changes when locked down

[PATCH v2 0/2] powerpc/pseries: restrict error injection and DT changes when locked down

[Nathan Lynch]

Add two new lockdown reasons for use in powerpc's pseries platform
code.

The pseries platform allows hardware-level error injection via certain
calls to the RTAS (Run Time Abstraction Services) firmware. ACPI-based
error injection is already restricted in lockdown; this facility
should be restricted for the same reasons.

pseries also allows nearly arbitrary device tree changes via
/proc/powerpc/ofdt. Just as overriding ACPI tables is not allowed
while locked down, so should this facility be restricted.

Changes since v1:
* Move LOCKDOWN_DEVICE_TREE next to LOCKDOWN_ACPI_TABLES.

Nathan Lynch (2):
  powerpc/pseries: block untrusted device tree changes when locked down
  powerpc/rtas: block error injection when locked down

 arch/powerpc/kernel/rtas.c                | 25 ++++++++++++++++++++++-
 arch/powerpc/platforms/pseries/reconfig.c |  5 +++++
 include/linux/security.h                  |  2 ++
 security/security.c                       |  2 ++
 4 files changed, 33 insertions(+), 1 deletion(-)

-- 
2.37.3

[PATCH v2 1/2] powerpc/pseries: block untrusted device tree changes when locked down

[Nathan Lynch]

The /proc/powerpc/ofdt interface allows the root user to freely alter
the in-kernel device tree, enabling arbitrary physical address writes
via drivers that could bind to malicious device nodes, thus making it
possible to disable lockdown.

Historically this interface has been used on the pseries platform to
facilitate the runtime addition and removal of processor, memory, and
device resources (aka Dynamic Logical Partitioning or DLPAR). Years
ago, the processor and memory use cases were migrated to designs that
happen to be lockdown-friendly: device tree updates are communicated
directly to the kernel from firmware without passing through untrusted
user space. I/O device DLPAR via the "drmgr" command in powerpc-utils
remains the sole legitimate user of /proc/powerpc/ofdt, but it is
already broken in lockdown since it uses /dev/mem to allocate argument
buffers for the rtas syscall. So only illegitimate uses of the
interface should see a behavior change when running on a locked down
kernel.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
---
 arch/powerpc/platforms/pseries/reconfig.c | 5 +++++
 include/linux/security.h                  | 1 +
 security/security.c                       | 1 +
 3 files changed, 7 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/reconfig.c b/arch/powerpc/platforms/pseries/reconfig.c
index cad7a0c93117..599bd2c78514 100644
--- a/arch/powerpc/platforms/pseries/reconfig.c
+++ b/arch/powerpc/platforms/pseries/reconfig.c
@@ -10,6 +10,7 @@
 #include <linux/kernel.h>
 #include <linux/notifier.h>
 #include <linux/proc_fs.h>
+#include <linux/security.h>
 #include <linux/slab.h>
 #include <linux/of.h>
 
@@ -361,6 +362,10 @@ static ssize_t ofdt_write(struct file *file, const char __user *buf, size_t coun
 	char *kbuf;
 	char *tmp;
 
+	rv = security_locked_down(LOCKDOWN_DEVICE_TREE);
+	if (rv)
+		return rv;
+
 	kbuf = memdup_user_nul(buf, count);
 	if (IS_ERR(kbuf))
 		return PTR_ERR(kbuf);
diff --git a/include/linux/security.h b/include/linux/security.h
index 7bd0c490703d..39e7c0e403d9 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -114,6 +114,7 @@ enum lockdown_reason {
 	LOCKDOWN_IOPORT,
 	LOCKDOWN_MSR,
 	LOCKDOWN_ACPI_TABLES,
+	LOCKDOWN_DEVICE_TREE,
 	LOCKDOWN_PCMCIA_CIS,
 	LOCKDOWN_TIOCSSERIAL,
 	LOCKDOWN_MODULE_PARAMETERS,
diff --git a/security/security.c b/security/security.c
index 4b95de24bc8d..51bf66d4f472 100644
--- a/security/security.c
+++ b/security/security.c
@@ -52,6 +52,7 @@ const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
 	[LOCKDOWN_IOPORT] = "raw io port access",
 	[LOCKDOWN_MSR] = "raw MSR access",
 	[LOCKDOWN_ACPI_TABLES] = "modifying ACPI tables",
+	[LOCKDOWN_DEVICE_TREE] = "modifying device tree contents",
 	[LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
 	[LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
 	[LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
-- 
2.37.3

Re: [PATCH v2 1/2] powerpc/pseries: block untrusted device tree changes when locked down

[Paul Moore]

On Mon, Sep 26, 2022 at 9:17 AM Nathan Lynch <nathanl@linux.ibm.com> wrote:
>
> The /proc/powerpc/ofdt interface allows the root user to freely alter
> the in-kernel device tree, enabling arbitrary physical address writes
> via drivers that could bind to malicious device nodes, thus making it
> possible to disable lockdown.
>
> Historically this interface has been used on the pseries platform to
> facilitate the runtime addition and removal of processor, memory, and
> device resources (aka Dynamic Logical Partitioning or DLPAR). Years
> ago, the processor and memory use cases were migrated to designs that
> happen to be lockdown-friendly: device tree updates are communicated
> directly to the kernel from firmware without passing through untrusted
> user space. I/O device DLPAR via the "drmgr" command in powerpc-utils
> remains the sole legitimate user of /proc/powerpc/ofdt, but it is
> already broken in lockdown since it uses /dev/mem to allocate argument
> buffers for the rtas syscall. So only illegitimate uses of the
> interface should see a behavior change when running on a locked down
> kernel.
>
> Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/reconfig.c | 5 +++++
>  include/linux/security.h                  | 1 +
>  security/security.c                       | 1 +
>  3 files changed, 7 insertions(+)

Thanks for moving the definitions.

Acked-by: Paul Moore <paul@paul-moore.com> (LSM)

> diff --git a/arch/powerpc/platforms/pseries/reconfig.c b/arch/powerpc/platforms/pseries/reconfig.c
> index cad7a0c93117..599bd2c78514 100644
> --- a/arch/powerpc/platforms/pseries/reconfig.c
> +++ b/arch/powerpc/platforms/pseries/reconfig.c
> @@ -10,6 +10,7 @@
>  #include <linux/kernel.h>
>  #include <linux/notifier.h>
>  #include <linux/proc_fs.h>
> +#include <linux/security.h>
>  #include <linux/slab.h>
>  #include <linux/of.h>
>
> @@ -361,6 +362,10 @@ static ssize_t ofdt_write(struct file *file, const char __user *buf, size_t coun
>         char *kbuf;
>         char *tmp;
>
> +       rv = security_locked_down(LOCKDOWN_DEVICE_TREE);
> +       if (rv)
> +               return rv;
> +
>         kbuf = memdup_user_nul(buf, count);
>         if (IS_ERR(kbuf))
>                 return PTR_ERR(kbuf);
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 7bd0c490703d..39e7c0e403d9 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -114,6 +114,7 @@ enum lockdown_reason {
>         LOCKDOWN_IOPORT,
>         LOCKDOWN_MSR,
>         LOCKDOWN_ACPI_TABLES,
> +       LOCKDOWN_DEVICE_TREE,
>         LOCKDOWN_PCMCIA_CIS,
>         LOCKDOWN_TIOCSSERIAL,
>         LOCKDOWN_MODULE_PARAMETERS,
> diff --git a/security/security.c b/security/security.c
> index 4b95de24bc8d..51bf66d4f472 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -52,6 +52,7 @@ const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
>         [LOCKDOWN_IOPORT] = "raw io port access",
>         [LOCKDOWN_MSR] = "raw MSR access",
>         [LOCKDOWN_ACPI_TABLES] = "modifying ACPI tables",
> +       [LOCKDOWN_DEVICE_TREE] = "modifying device tree contents",
>         [LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
>         [LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
>         [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
> --
> 2.37.3
>


-- 
paul-moore.com

Re: [PATCH v2 1/2] powerpc/pseries: block untrusted device tree changes when locked down

[Andrew Donnellan]

On Mon, 2022-09-26 at 08:16 -0500, Nathan Lynch wrote:
> The /proc/powerpc/ofdt interface allows the root user to freely alter
> the in-kernel device tree, enabling arbitrary physical address writes
> via drivers that could bind to malicious device nodes, thus making it
> possible to disable lockdown.
> 
> Historically this interface has been used on the pseries platform to
> facilitate the runtime addition and removal of processor, memory, and
> device resources (aka Dynamic Logical Partitioning or DLPAR). Years
> ago, the processor and memory use cases were migrated to designs that
> happen to be lockdown-friendly: device tree updates are communicated
> directly to the kernel from firmware without passing through
> untrusted
> user space. I/O device DLPAR via the "drmgr" command in powerpc-utils
> remains the sole legitimate user of /proc/powerpc/ofdt, but it is
> already broken in lockdown since it uses /dev/mem to allocate
> argument
> buffers for the rtas syscall. So only illegitimate uses of the
> interface should see a behavior change when running on a locked down
> kernel.
> 
> Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>

Seems sensible to me.

Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>

> ---
>  arch/powerpc/platforms/pseries/reconfig.c | 5 +++++
>  include/linux/security.h                  | 1 +
>  security/security.c                       | 1 +
>  3 files changed, 7 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/pseries/reconfig.c
> b/arch/powerpc/platforms/pseries/reconfig.c
> index cad7a0c93117..599bd2c78514 100644
> --- a/arch/powerpc/platforms/pseries/reconfig.c
> +++ b/arch/powerpc/platforms/pseries/reconfig.c
> @@ -10,6 +10,7 @@
>  #include <linux/kernel.h>
>  #include <linux/notifier.h>
>  #include <linux/proc_fs.h>
> +#include <linux/security.h>
>  #include <linux/slab.h>
>  #include <linux/of.h>
>  
> @@ -361,6 +362,10 @@ static ssize_t ofdt_write(struct file *file,
> const char __user *buf, size_t coun
>         char *kbuf;
>         char *tmp;
>  
> +       rv = security_locked_down(LOCKDOWN_DEVICE_TREE);
> +       if (rv)
> +               return rv;
> +
>         kbuf = memdup_user_nul(buf, count);
>         if (IS_ERR(kbuf))
>                 return PTR_ERR(kbuf);
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 7bd0c490703d..39e7c0e403d9 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -114,6 +114,7 @@ enum lockdown_reason {
>         LOCKDOWN_IOPORT,
>         LOCKDOWN_MSR,
>         LOCKDOWN_ACPI_TABLES,
> +       LOCKDOWN_DEVICE_TREE,
>         LOCKDOWN_PCMCIA_CIS,
>         LOCKDOWN_TIOCSSERIAL,
>         LOCKDOWN_MODULE_PARAMETERS,
> diff --git a/security/security.c b/security/security.c
> index 4b95de24bc8d..51bf66d4f472 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -52,6 +52,7 @@ const char *const
> lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
>         [LOCKDOWN_IOPORT] = "raw io port access",
>         [LOCKDOWN_MSR] = "raw MSR access",
>         [LOCKDOWN_ACPI_TABLES] = "modifying ACPI tables",
> +       [LOCKDOWN_DEVICE_TREE] = "modifying device tree contents",
>         [LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
>         [LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
>         [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@linux.ibm.com   IBM Australia Limited

[PATCH v2 2/2] powerpc/rtas: block error injection when locked down

[Nathan Lynch]

The error injection facility on pseries VMs allows corruption of
arbitrary guest memory, potentially enabling a sufficiently privileged
user to disable lockdown or perform other modifications of the running
kernel via the rtas syscall.

Block the PAPR error injection facility from being opened or called
when locked down.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
---
 arch/powerpc/kernel/rtas.c | 25 ++++++++++++++++++++++++-
 include/linux/security.h   |  1 +
 security/security.c        |  1 +
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 693133972294..c2540d393f1c 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -23,6 +23,7 @@
 #include <linux/memblock.h>
 #include <linux/slab.h>
 #include <linux/reboot.h>
+#include <linux/security.h>
 #include <linux/syscalls.h>
 #include <linux/of.h>
 #include <linux/of_fdt.h>
@@ -464,6 +465,9 @@ void rtas_call_unlocked(struct rtas_args *args, int token, int nargs, int nret,
 	va_end(list);
 }
 
+static int ibm_open_errinjct_token;
+static int ibm_errinjct_token;
+
 int rtas_call(int token, int nargs, int nret, int *outputs, ...)
 {
 	va_list list;
@@ -476,6 +480,16 @@ int rtas_call(int token, int nargs, int nret, int *outputs, ...)
 	if (!rtas.entry || token == RTAS_UNKNOWN_SERVICE)
 		return -1;
 
+	if (token == ibm_open_errinjct_token || token == ibm_errinjct_token) {
+		/*
+		 * It would be nicer to not discard the error value
+		 * from security_locked_down(), but callers expect an
+		 * RTAS status, not an errno.
+		 */
+		if (security_locked_down(LOCKDOWN_RTAS_ERROR_INJECTION))
+			return -1;
+	}
+
 	if ((mfmsr() & (MSR_IR|MSR_DR)) != (MSR_IR|MSR_DR)) {
 		WARN_ON_ONCE(1);
 		return -1;
@@ -1227,6 +1241,14 @@ SYSCALL_DEFINE1(rtas, struct rtas_args __user *, uargs)
 	if (block_rtas_call(token, nargs, &args))
 		return -EINVAL;
 
+	if (token == ibm_open_errinjct_token || token == ibm_errinjct_token) {
+		int err;
+
+		err = security_locked_down(LOCKDOWN_RTAS_ERROR_INJECTION);
+		if (err)
+			return err;
+	}
+
 	/* Need to handle ibm,suspend_me call specially */
 	if (token == rtas_token("ibm,suspend-me")) {
 
@@ -1325,7 +1347,8 @@ void __init rtas_initialize(void)
 #ifdef CONFIG_RTAS_ERROR_LOGGING
 	rtas_last_error_token = rtas_token("rtas-last-error");
 #endif
-
+	ibm_open_errinjct_token = rtas_token("ibm,open-errinjct");
+	ibm_errinjct_token = rtas_token("ibm,errinjct");
 	rtas_syscall_filter_init();
 }
 
diff --git a/include/linux/security.h b/include/linux/security.h
index 39e7c0e403d9..70f89dc3a712 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -123,6 +123,7 @@ enum lockdown_reason {
 	LOCKDOWN_XMON_WR,
 	LOCKDOWN_BPF_WRITE_USER,
 	LOCKDOWN_DBG_WRITE_KERNEL,
+	LOCKDOWN_RTAS_ERROR_INJECTION,
 	LOCKDOWN_INTEGRITY_MAX,
 	LOCKDOWN_KCORE,
 	LOCKDOWN_KPROBES,
diff --git a/security/security.c b/security/security.c
index 51bf66d4f472..eabe3ce7e74e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -61,6 +61,7 @@ const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
 	[LOCKDOWN_XMON_WR] = "xmon write access",
 	[LOCKDOWN_BPF_WRITE_USER] = "use of bpf to write user RAM",
 	[LOCKDOWN_DBG_WRITE_KERNEL] = "use of kgdb/kdb to write kernel RAM",
+	[LOCKDOWN_RTAS_ERROR_INJECTION] = "RTAS error injection",
 	[LOCKDOWN_INTEGRITY_MAX] = "integrity",
 	[LOCKDOWN_KCORE] = "/proc/kcore access",
 	[LOCKDOWN_KPROBES] = "use of kprobes",
-- 
2.37.3

Re: [PATCH v2 2/2] powerpc/rtas: block error injection when locked down

[Paul Moore]

On Mon, Sep 26, 2022 at 9:18 AM Nathan Lynch <nathanl@linux.ibm.com> wrote:
>
> The error injection facility on pseries VMs allows corruption of
> arbitrary guest memory, potentially enabling a sufficiently privileged
> user to disable lockdown or perform other modifications of the running
> kernel via the rtas syscall.
>
> Block the PAPR error injection facility from being opened or called
> when locked down.
>
> Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
> ---
>  arch/powerpc/kernel/rtas.c | 25 ++++++++++++++++++++++++-
>  include/linux/security.h   |  1 +
>  security/security.c        |  1 +
>  3 files changed, 26 insertions(+), 1 deletion(-)

The lockdown changes are trivial, but they look fine to me.

Acked-by: Paul Moore <paul@paul-moore.com> (LSM)

-- 
paul-moore.com

Re: [PATCH v2 2/2] powerpc/rtas: block error injection when locked down

[Andrew Donnellan]

On Mon, 2022-09-26 at 08:16 -0500, Nathan Lynch wrote:
> The error injection facility on pseries VMs allows corruption of
> arbitrary guest memory, potentially enabling a sufficiently
> privileged
> user to disable lockdown or perform other modifications of the
> running
> kernel via the rtas syscall.
> 
> Block the PAPR error injection facility from being opened or called
> when locked down.
> 
> Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>

Is there any circumstance (short of arbitrary code execution etc) where
the rtas_call() check will actually trigger rather than the sys_rtas()
check? (Not that it matters, defence in depth is good.)

Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>

> ---
>  arch/powerpc/kernel/rtas.c | 25 ++++++++++++++++++++++++-
>  include/linux/security.h   |  1 +
>  security/security.c        |  1 +
>  3 files changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index 693133972294..c2540d393f1c 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -23,6 +23,7 @@
>  #include <linux/memblock.h>
>  #include <linux/slab.h>
>  #include <linux/reboot.h>
> +#include <linux/security.h>
>  #include <linux/syscalls.h>
>  #include <linux/of.h>
>  #include <linux/of_fdt.h>
> @@ -464,6 +465,9 @@ void rtas_call_unlocked(struct rtas_args *args,
> int token, int nargs, int nret,
>         va_end(list);
>  }
>  
> +static int ibm_open_errinjct_token;
> +static int ibm_errinjct_token;
> +
>  int rtas_call(int token, int nargs, int nret, int *outputs, ...)
>  {
>         va_list list;
> @@ -476,6 +480,16 @@ int rtas_call(int token, int nargs, int nret,
> int *outputs, ...)
>         if (!rtas.entry || token == RTAS_UNKNOWN_SERVICE)
>                 return -1;
>  
> +       if (token == ibm_open_errinjct_token || token ==
> ibm_errinjct_token) {
> +               /*
> +                * It would be nicer to not discard the error value
> +                * from security_locked_down(), but callers expect an
> +                * RTAS status, not an errno.
> +                */
> +               if
> (security_locked_down(LOCKDOWN_RTAS_ERROR_INJECTION))
> +                       return -1;
> +       }
> +
>         if ((mfmsr() & (MSR_IR|MSR_DR)) != (MSR_IR|MSR_DR)) {
>                 WARN_ON_ONCE(1);
>                 return -1;
> @@ -1227,6 +1241,14 @@ SYSCALL_DEFINE1(rtas, struct rtas_args __user
> *, uargs)
>         if (block_rtas_call(token, nargs, &args))
>                 return -EINVAL;
>  
> +       if (token == ibm_open_errinjct_token || token ==
> ibm_errinjct_token) {
> +               int err;
> +
> +               err =
> security_locked_down(LOCKDOWN_RTAS_ERROR_INJECTION);
> +               if (err)
> +                       return err;
> +       }
> +
>         /* Need to handle ibm,suspend_me call specially */
>         if (token == rtas_token("ibm,suspend-me")) {
>  
> @@ -1325,7 +1347,8 @@ void __init rtas_initialize(void)
>  #ifdef CONFIG_RTAS_ERROR_LOGGING
>         rtas_last_error_token = rtas_token("rtas-last-error");
>  #endif
> -
> +       ibm_open_errinjct_token = rtas_token("ibm,open-errinjct");
> +       ibm_errinjct_token = rtas_token("ibm,errinjct");
>         rtas_syscall_filter_init();
>  }
>  
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 39e7c0e403d9..70f89dc3a712 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -123,6 +123,7 @@ enum lockdown_reason {
>         LOCKDOWN_XMON_WR,
>         LOCKDOWN_BPF_WRITE_USER,
>         LOCKDOWN_DBG_WRITE_KERNEL,
> +       LOCKDOWN_RTAS_ERROR_INJECTION,
>         LOCKDOWN_INTEGRITY_MAX,
>         LOCKDOWN_KCORE,
>         LOCKDOWN_KPROBES,
> diff --git a/security/security.c b/security/security.c
> index 51bf66d4f472..eabe3ce7e74e 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -61,6 +61,7 @@ const char *const
> lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
>         [LOCKDOWN_XMON_WR] = "xmon write access",
>         [LOCKDOWN_BPF_WRITE_USER] = "use of bpf to write user RAM",
>         [LOCKDOWN_DBG_WRITE_KERNEL] = "use of kgdb/kdb to write
> kernel RAM",
> +       [LOCKDOWN_RTAS_ERROR_INJECTION] = "RTAS error injection",
>         [LOCKDOWN_INTEGRITY_MAX] = "integrity",
>         [LOCKDOWN_KCORE] = "/proc/kcore access",
>         [LOCKDOWN_KPROBES] = "use of kprobes",

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@linux.ibm.com   IBM Australia Limited

Re: [PATCH v2 2/2] powerpc/rtas: block error injection when locked down

[Nathan Lynch]

Andrew Donnellan <ajd@linux.ibm.com> writes:

> On Mon, 2022-09-26 at 08:16 -0500, Nathan Lynch wrote:
>> The error injection facility on pseries VMs allows corruption of
>> arbitrary guest memory, potentially enabling a sufficiently
>> privileged
>> user to disable lockdown or perform other modifications of the
>> running
>> kernel via the rtas syscall.
>> 
>> Block the PAPR error injection facility from being opened or called
>> when locked down.
>> 
>> Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
>
> Is there any circumstance (short of arbitrary code execution etc) where
> the rtas_call() check will actually trigger rather than the sys_rtas()
> check? (Not that it matters, defence in depth is good.)

Fair question! There are no in-kernel users of rtas_call() that pass the
error injection tokens as far as I could tell. Nor am I aware of any
out-of-tree users, for that matter. But rtas_call() is the likely most
appropriate place to have the lockdown gate should that situation change
(as it might, see https://github.com/ibm-power-utilities/librtas/issues/29).

Re: [PATCH v2 0/2] powerpc/pseries: restrict error injection and DT changes when locked down

[Michael Ellerman]

On Mon, 26 Sep 2022 08:16:41 -0500, Nathan Lynch wrote:
> Add two new lockdown reasons for use in powerpc's pseries platform
> code.
> 
> The pseries platform allows hardware-level error injection via certain
> calls to the RTAS (Run Time Abstraction Services) firmware. ACPI-based
> error injection is already restricted in lockdown; this facility
> should be restricted for the same reasons.
> 
> [...]

Applied to powerpc/next.

[1/2] powerpc/pseries: block untrusted device tree changes when locked down
      https://git.kernel.org/powerpc/c/99df7a2810b6d24651d4887ab61a142e042fb235
[2/2] powerpc/rtas: block error injection when locked down
      https://git.kernel.org/powerpc/c/b8f3e48834fe8c86b4f21739c6effd160e2c2c19

cheers