linux-kernel - [PATCH 6.6.y] powerpc/rtas: Prevent Spectre v1 gadget construction in sys

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Message-Id: <20250411064213.3647619-1-donghua.liu@windriver.com>
Date: Fri, 11 Apr 2025 14:42:13 +0800
From: Cliff Liu <donghua.liu@...driver.com>
To: stable@...r.kernel.org
Cc: mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu,
        leitao@...ian.org, nathanl@...ux.ibm.com, donghua.liu@...driver.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Zhe.He@...driver.com
Subject: [PATCH 6.6.y] powerpc/rtas: Prevent Spectre v1 gadget construction in sys_rtas()

From: Nathan Lynch <nathanl@...ux.ibm.com>

[ Upstream commit 0974d03eb479384466d828d65637814bee6b26d7 ]

Smatch warns:

  arch/powerpc/kernel/rtas.c:1932 __do_sys_rtas() warn: potential
  spectre issue 'args.args' [r] (local cap)

The 'nargs' and 'nret' locals come directly from a user-supplied
buffer and are used as indexes into a small stack-based array and as
inputs to copy_to_user() after they are subject to bounds checks.

Use array_index_nospec() after the bounds checks to clamp these values
for speculative execution.

Signed-off-by: Nathan Lynch <nathanl@...ux.ibm.com>
Reported-by: Breno Leitao <leitao@...ian.org>
Reviewed-by: Breno Leitao <leitao@...ian.org>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://msgid.link/20240530-sys_rtas-nargs-nret-v1-1-129acddd4d89@linux.ibm.com
[Minor context change fixed]
Signed-off-by: Cliff Liu <donghua.liu@...driver.com>
Signed-off-by: He Zhe <Zhe.He@...driver.com>
---
Verified the powerpc build test.
---
 arch/powerpc/kernel/rtas.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 46b9476d7582..dc294c95da21 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -18,6 +18,7 @@
 #include <linux/kernel.h>
 #include <linux/lockdep.h>
 #include <linux/memblock.h>
+#include <linux/nospec.h>
 #include <linux/of.h>
 #include <linux/of_fdt.h>
 #include <linux/reboot.h>
@@ -1839,6 +1840,9 @@ SYSCALL_DEFINE1(rtas, struct rtas_args __user *, uargs)
 	    || nargs + nret > ARRAY_SIZE(args.args))
 		return -EINVAL;
 
+	nargs = array_index_nospec(nargs, ARRAY_SIZE(args.args));
+	nret = array_index_nospec(nret, ARRAY_SIZE(args.args) - nargs);
+
 	/* Copy in args. */
 	if (copy_from_user(args.args, uargs->args,
 			   nargs * sizeof(rtas_arg_t)) != 0)
-- 
2.34.1