linux-kernel - [PATCH 2/4] x86/signal: Use switch_to_permissive_pkey

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Message-ID: <6a97e9986b0fb05935204f55f8d16fc5e66f0ccf.1739790300.git.dvyukov@google.com>
Date: Mon, 17 Feb 2025 12:07:31 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: mathieu.desnoyers@...icios.com, peterz@...radead.org, boqun.feng@...il.com, 
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, hpa@...or.com, aruna.ramakrishna@...cle.com, 
	elver@...gle.com
Cc: Dmitry Vyukov <dvyukov@...gle.com>, "Paul E. McKenney" <paulmck@...nel.org>, x86@...nel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/4] x86/signal: Use switch_to_permissive_pkey_reg() helper

Use the new switch_to_permissive_pkey_reg() helper instead of the
custom code. No functional changes intended.

Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
Cc: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
---
 arch/x86/kernel/signal.c | 33 +++++++++++++--------------------
 1 file changed, 13 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 5f441039b5725..b753de278257a 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -28,6 +28,7 @@
 #include <linux/entry-common.h>
 #include <linux/syscalls.h>
 #include <linux/rseq.h>
+#include <linux/pkeys.h>
 
 #include <asm/processor.h>
 #include <asm/ucontext.h>
@@ -60,24 +61,6 @@ static inline int is_x32_frame(struct ksignal *ksig)
 		ksig->ka.sa.sa_flags & SA_X32_ABI;
 }
 
-/*
- * Enable all pkeys temporarily, so as to ensure that both the current
- * execution stack as well as the alternate signal stack are writeable.
- * The application can use any of the available pkeys to protect the
- * alternate signal stack, and we don't know which one it is, so enable
- * all. The PKRU register will be reset to init_pkru later in the flow,
- * in fpu__clear_user_states(), and it is the application's responsibility
- * to enable the appropriate pkey as the first step in the signal handler
- * so that the handler does not segfault.
- */
-static inline u32 sig_prepare_pkru(void)
-{
-	u32 orig_pkru = read_pkru();
-
-	write_pkru(0);
-	return orig_pkru;
-}
-
 /*
  * Set up a signal frame.
  */
@@ -157,8 +140,18 @@ get_sigframe(struct ksignal *ksig, struct pt_regs *regs, size_t frame_size,
 		return (void __user *)-1L;
 	}
 
-	/* Update PKRU to enable access to the alternate signal stack. */
-	pkru = sig_prepare_pkru();
+	/*
+	 * Enable all pkeys temporarily, so as to ensure that both the current
+	 * execution stack as well as the alternate signal stack are
+	 * writeable. The application can use any of the available pkeys to
+	 * protect the alternate signal stack, and we don't know which one it
+	 * is, so enable all. The PKRU register will be reset to init_pkru
+	 * later in the flow, in fpu__clear_user_states(), and it is the
+	 * application's responsibility to enable the appropriate pkey as the
+	 * first step in the signal handler so that the handler does not
+	 * segfault.
+	 */
+	pkru = switch_to_permissive_pkey_reg();
 	/* save i387 and extended state */
 	if (!copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size, pkru)) {
 		/*
-- 
2.48.1.601.g30ceb7b040-goog