linux-kernel - [tip: x86/urgent] x86/fpu/signal: Initialize sw_bytes in save_xstate

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Message-ID: <163831455793.11128.4485814974540705191.tip-bot2@tip-bot2>
Date:   Tue, 30 Nov 2021 23:22:37 -0000
From:   "tip-bot2 for Marco Elver" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/fpu/signal: Initialize sw_bytes in save_xstate_epilog()

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     52d0b8b18776f184c53632c5e0068201491cdb61
Gitweb:        https://git.kernel.org/tip/52d0b8b18776f184c53632c5e0068201491cdb61
Author:        Marco Elver <elver@...gle.com>
AuthorDate:    Fri, 26 Nov 2021 13:47:46 +01:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Tue, 30 Nov 2021 15:13:47 -08:00

x86/fpu/signal: Initialize sw_bytes in save_xstate_epilog()

save_sw_bytes() did not fully initialize sw_bytes, which caused KMSAN
to report an infoleak (see below).
Initialize sw_bytes explicitly to avoid this.

KMSAN report follows:

=====================================================
BUG: KMSAN: kernel-infoleak in instrument_copy_to_user ./include/linux/instrumented.h:121
BUG: KMSAN: kernel-infoleak in __copy_to_user ./include/linux/uaccess.h:154
BUG: KMSAN: kernel-infoleak in save_xstate_epilog+0x2df/0x510 arch/x86/kernel/fpu/signal.c:127
 instrument_copy_to_user ./include/linux/instrumented.h:121
 __copy_to_user ./include/linux/uaccess.h:154
 save_xstate_epilog+0x2df/0x510 arch/x86/kernel/fpu/signal.c:127
 copy_fpstate_to_sigframe+0x861/0xb60 arch/x86/kernel/fpu/signal.c:245
 get_sigframe+0x656/0x7e0 arch/x86/kernel/signal.c:296
 __setup_rt_frame+0x14d/0x2a60 arch/x86/kernel/signal.c:471
 setup_rt_frame arch/x86/kernel/signal.c:781
 handle_signal arch/x86/kernel/signal.c:825
 arch_do_signal_or_restart+0x417/0xdd0 arch/x86/kernel/signal.c:870
 handle_signal_work kernel/entry/common.c:149
 exit_to_user_mode_loop+0x1f6/0x490 kernel/entry/common.c:173
 exit_to_user_mode_prepare kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290
 syscall_exit_to_user_mode+0x7e/0xc0 kernel/entry/common.c:302
 do_syscall_64+0x60/0xd0 arch/x86/entry/common.c:88
 entry_SYSCALL_64_after_hwframe+0x44/0xae ??:?

Local variable sw_bytes created at:
 save_xstate_epilog+0x80/0x510 arch/x86/kernel/fpu/signal.c:121
 copy_fpstate_to_sigframe+0x861/0xb60 arch/x86/kernel/fpu/signal.c:245

Bytes 20-47 of 48 are uninitialized
Memory access of size 48 starts at ffff8880801d3a18
Data copied to user address 00007ffd90e2ef50
=====================================================

Link: https://lore.kernel.org/all/CAG_fn=V9T6OKPonSjsi9PmWB0hMHFC=yawozdft8i1-MSxrv=w@mail.gmail.com/
Fixes: 53599b4d54b9b8dd ("x86/fpu/signal: Prepare for variable sigframe length")
Reported-by: Alexander Potapenko <glider@...gle.com>
Signed-off-by: Marco Elver <elver@...gle.com>
Signed-off-by: Alexander Potapenko <glider@...gle.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Tested-by: Alexander Potapenko <glider@...gle.com>
Link: https://lkml.kernel.org/r/20211126124746.761278-1-glider@google.com
---
 arch/x86/kernel/fpu/signal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index d595827..91d4b6d 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -118,7 +118,7 @@ static inline bool save_xstate_epilog(void __user *buf, int ia32_frame,
 				      struct fpstate *fpstate)
 {
 	struct xregs_state __user *x = buf;
-	struct _fpx_sw_bytes sw_bytes;
+	struct _fpx_sw_bytes sw_bytes = {};
 	u32 xfeatures;
 	int err;