2021-06-17 02:16:19

by Kees Cook

Subject: [PATCH] s390/speculation: Use statically initialized const for instructions

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
confusing the checks when using a static const source.

Move the static const array into a variable so the compiler can perform
appropriate bounds checking.

Signed-off-by: Kees Cook <[email protected]>
---
arch/s390/kernel/nospec-branch.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kernel/nospec-branch.c b/arch/s390/kernel/nospec-branch.c
index 2c5c3756644b..250e4dbf653c 100644
--- a/arch/s390/kernel/nospec-branch.c
+++ b/arch/s390/kernel/nospec-branch.c
@@ -99,6 +99,7 @@ early_param("spectre_v2", spectre_v2_setup_early);
static void __init_or_module __nospec_revert(s32 *start, s32 *end)
{
enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
+ static const u8 branch[] = { 0x47, 0x00, 0x07, 0x00 };
u8 *instr, *thunk, *br;
u8 insnbuf[6];
s32 *epo;
@@ -128,7 +129,7 @@ static void __init_or_module __nospec_revert(s32 *start, s32 *end)
if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
continue;

- memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
+ memcpy(insnbuf + 2, branch, sizeof(branch));
switch (type) {
case BRCL_EXPOLINE:
insnbuf[0] = br[0];
--
2.25.1

2021-06-22 14:18:31

by Vasily Gorbik

Subject: Re: [PATCH] s390/speculation: Use statically initialized const for instructions

On Wed, Jun 16, 2021 at 01:18:23PM -0700, Kees Cook wrote:
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), memmove(), and memset(), avoid
> confusing the checks when using a static const source.
>
> Move the static const array into a variable so the compiler can perform
> appropriate bounds checking.
>
> Signed-off-by: Kees Cook <[email protected]>
> ---
> arch/s390/kernel/nospec-branch.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)

Applied, thanks!