Subject: [PATCH 09/13] powerpc/rtas: mandate RTAS syscall filtering

From: Nathan Lynch <[email-masked]>
Date: Fri, 18 Nov 2022 09:07:47 -0600

CONFIG_PPC_RTAS_FILTER has been optional but default-enabled since its
introduction. It's been enabled in enterprise distro kernels for a
while without causing ABI breakage that wasn't easily fixed, and it
prevents harmful abuses of the rtas syscall.

Let's make it unconditional.

Signed-off-by: Nathan Lynch <[email-masked]>
---
 arch/powerpc/Kconfig       | 13 -------------
 arch/powerpc/kernel/rtas.c | 16 ----------------
 2 files changed, 29 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2ca5418457ed..8092915a4e9b 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -1012,19 +1012,6 @@ config PPC_SECVAR_SYSFS
 	  read/write operations on these variables. Say Y if you have
 	  secure boot enabled and want to expose variables to userspace.
 
-config PPC_RTAS_FILTER
-	bool "Enable filtering of RTAS syscalls"
-	default y
-	depends on PPC_RTAS
-	help
-	  The RTAS syscall API has security issues that could be used to
-	  compromise system integrity. This option enforces restrictions on the
-	  RTAS calls and arguments passed by userspace programs to mitigate
-	  these issues.
-
-	  Say Y unless you know what you are doing and the filter is causing
-	  problems for you.
-
 endmenu
 
 config ISA_DMA_API
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index c3142d352f41..3929bcea92c0 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -1051,8 +1051,6 @@ noinstr struct pseries_errorlog *get_pseries_errorlog(struct rtas_error_log *log
 	return NULL;
 }
 
-#ifdef CONFIG_PPC_RTAS_FILTER
-
 /*
  * The sys_rtas syscall, as originally designed, allows root to pass
  * arbitrary physical addresses to RTAS calls. A number of RTAS calls
@@ -1201,20 +1199,6 @@ static void __init rtas_syscall_filter_init(void)
 		rtas_filters[i].token = rtas_token(rtas_filters[i].name);
 }
 
-#else
-
-static bool block_rtas_call(int token, int nargs,
-			    struct rtas_args *args)
-{
-	return false;
-}
-
-static void __init rtas_syscall_filter_init(void)
-{
-}
-
-#endif /* CONFIG_PPC_RTAS_FILTER */
-
 /* We assume to be passed big endian arguments */
 SYSCALL_DEFINE1(rtas, struct rtas_args __user *, uargs)
 {
-- 
2.37.1