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 <nath...@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 <a...@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
a...@linux.ibm.com IBM Australia Limited
