[PATCH] powerpc/rtas: Prevent Spectre v1 gadget construction in sys_rtas()

[PATCH] powerpc/rtas: Prevent Spectre v1 gadget construction in sys_rtas()

[haixiao.yan.cn]

From: Nathan Lynch <nathanl@linux.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@linux.ibm.com>
Reported-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240530-sys_rtas-nargs-nret-v1-1-129acddd4d89@linux.ibm.com
Signed-off-by: Haixiao Yan <haixiao.yan.cn@windriver.com>
---
This commit is backporting 0974d03eb479 to the branch linux-5.15.y to
solve the CVE-2024-46774.

 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 d01a0ad57e38..f2378f51cbed 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -16,6 +16,7 @@
 #include <linux/capability.h>
 #include <linux/delay.h>
 #include <linux/cpu.h>
+#include <linux/nospec.h>
 #include <linux/sched.h>
 #include <linux/smp.h>
 #include <linux/completion.h>
@@ -1076,6 +1077,9 @@ 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)
-- 
2.35.5

Re: [PATCH] powerpc/rtas: Prevent Spectre v1 gadget construction in sys_rtas()

[Greg KH]

On Fri, Dec 13, 2024 at 11:44:22AM +0800, haixiao.yan.cn@eng.windriver.com wrote:
> From: Nathan Lynch <nathanl@linux.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@linux.ibm.com>
> Reported-by: Breno Leitao <leitao@debian.org>
> Reviewed-by: Breno Leitao <leitao@debian.org>
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> Link: https://msgid.link/20240530-sys_rtas-nargs-nret-v1-1-129acddd4d89@linux.ibm.com
> Signed-off-by: Haixiao Yan <haixiao.yan.cn@windriver.com>
> ---
> This commit is backporting 0974d03eb479 to the branch linux-5.15.y to
> solve the CVE-2024-46774.

Now deleted, please see:
	https://lore.kernel.org/r/2024121322-conjuror-gap-b542@gregkh
for what you all need to do, TOGETHER, to get this fixed and so that I
can accept patches from your company in the future.

thanks,

greg k-h

Re: [PATCH] powerpc/rtas: Prevent Spectre v1 gadget construction in sys_rtas()

[Greg KH]

On Fri, Dec 13, 2024 at 11:44:22AM +0800, haixiao.yan.cn@eng.windriver.com wrote:
> From: Nathan Lynch <nathanl@linux.ibm.com>
> 
> [ Upstream commit 0974d03eb479384466d828d65637814bee6b26d7 ]
> 


Now deleted, please see:
        https://lore.kernel.org/r/2024121322-conjuror-gap-b542@gregkh
for what you all need to do, TOGETHER, to get this fixed and so that I
can accept patches from your company in the future.

thanks,

greg k-h

Re: [PATCH] powerpc/rtas: Prevent Spectre v1 gadget construction in sys_rtas()

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

The upstream commit SHA1 provided is correct: 0974d03eb479384466d828d65637814bee6b26d7

WARNING: Author mismatch between patch and upstream commit:
Backport author: haixiao.yan.cn@eng.windriver.com
Commit author: Nathan Lynch <nathanl@linux.ibm.com>


Status in newer kernel trees:
6.12.y | Present (exact SHA1)

Note: The patch differs from the upstream commit:
---
Failed to apply patch cleanly, falling back to interdiff...
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.12.y       |  Failed     |  N/A       |
| stable/linux-6.6.y        |  Failed     |  N/A       |
| stable/linux-6.1.y        |  Success    |  Success   |
| stable/linux-5.15.y       |  Success    |  Success   |
| stable/linux-5.10.y       |  Success    |  Success   |
| stable/linux-5.4.y        |  Success    |  Success   |