linux-kernel - [PATCH] x86/shstk: Enable shadow stack for x32

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Message-ID: <20240315140433.1966543-1-hjl.tools@gmail.com>
Date: Fri, 15 Mar 2024 07:04:33 -0700
From: "H.J. Lu" <hjl.tools@...il.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org,
	Rick P Edgecombe <rick.p.edgecombe@...el.com>
Subject: [PATCH] x86/shstk: Enable shadow stack for x32

1. Add shadow stack support to x32 signal.
2. Use the 64-bit map_shadow_stack syscall for x32.
3. Set up shadow stack for x32.

Tested with shadow stack enabled x32 glibc on Intel Tiger Lake.

Cc: Rick P Edgecombe <rick.p.edgecombe@...el.com>
Tested-by: H.J. Lu <hjl.tools@...il.com>
Signed-off-by: H.J. Lu <hjl.tools@...il.com>
---
 arch/x86/entry/syscalls/syscall_64.tbl | 2 +-
 arch/x86/kernel/shstk.c                | 4 ++--
 arch/x86/kernel/signal_64.c            | 6 ++++++
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 7e8d46f4147f..cc78226ffc35 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -374,7 +374,7 @@
 450	common	set_mempolicy_home_node	sys_set_mempolicy_home_node
 451	common	cachestat		sys_cachestat
 452	common	fchmodat2		sys_fchmodat2
-453	64	map_shadow_stack	sys_map_shadow_stack
+453	common	map_shadow_stack	sys_map_shadow_stack
 454	common	futex_wake		sys_futex_wake
 455	common	futex_wait		sys_futex_wait
 456	common	futex_requeue		sys_futex_requeue
diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index 59e15dd8d0f8..6f1e9883f074 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -163,8 +163,8 @@ static int shstk_setup(void)
 	if (features_enabled(ARCH_SHSTK_SHSTK))
 		return 0;
 
-	/* Also not supported for 32 bit and x32 */
-	if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK) || in_32bit_syscall())
+	/* Also not supported for 32 bit */
+	if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK) || in_ia32_syscall())
 		return -EOPNOTSUPP;
 
 	size = adjust_shstk_size(0);
diff --git a/arch/x86/kernel/signal_64.c b/arch/x86/kernel/signal_64.c
index 23d8aaf8d9fd..8a94053c5444 100644
--- a/arch/x86/kernel/signal_64.c
+++ b/arch/x86/kernel/signal_64.c
@@ -315,6 +315,9 @@ int x32_setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs)
 
 	uc_flags = frame_uc_flags(regs);
 
+	if (setup_signal_shadow_stack(ksig))
+		return -EFAULT;
+
 	if (!user_access_begin(frame, sizeof(*frame)))
 		return -EFAULT;
 
@@ -377,6 +380,9 @@ COMPAT_SYSCALL_DEFINE0(x32_rt_sigreturn)
 	if (!restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
 		goto badframe;
 
+	if (restore_signal_shadow_stack())
+		goto badframe;
+
 	if (compat_restore_altstack(&frame->uc.uc_stack))
 		goto badframe;
 
-- 
2.44.0