linux-kernel - [PATCH 1/2] x86/pkeys: Change caller of update_pkru_in

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Message-ID: <20241114075241.3550166-1-aruna.ramakrishna@oracle.com>
Date: Thu, 14 Nov 2024 07:52:40 +0000
From: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, dave.hansen@...ux.intel.com, tglx@...utronix.de,
        mingo@...nel.org, rudi.horn@...cle.com, joe.jin@...cle.com
Subject: [PATCH 1/2] x86/pkeys: Change caller of update_pkru_in_sigframe()

The commit 70044df250d0 ("x86/pkeys: Update PKRU to enable all pkeys
before XSAVE") enables all pkeys before XSAVE to allow writing data
to the sigaltstack (i.e. it does a wrpkru(0)).

However, when PKRU is set to 0, it has the side effect of setting
XINUSE[PKRU] to 0 on AMD systems, but not on Intel - this in turn
sets XSTATE_BV[PKRU] to 0. XRSTOR will not restore the component i
from the XSAVE area if XSTATE_BV[i] is 0 - effectively ignoring the
value of PKRU updated on the sigframe by update_pkru_in_sigframe().
This means that PKRU stays at 0 when control is returned back to the
user after signal handling, which is unexpected.

To fix this, and to ensure that PKRU is always restored correctly
from the XSAVE data on both Intel and AMD systems, explicitly set
XSTATE_BV[PKRU] to 1.

This change is split into 2 patches - the first one merely changes
the caller of update_pkru_in_sigframe(), but the behavior remains
the same. The next patch will update the XSTATE_BV bit for PKRU.

No functional changes.

Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
---
 arch/x86/kernel/fpu/signal.c | 20 ++------------------
 arch/x86/kernel/fpu/xstate.h | 15 ++++++++++++++-
 2 files changed, 16 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 1065ab995305..8f62e0666dea 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -63,16 +63,6 @@ static inline bool check_xstate_in_sigframe(struct fxregs_state __user *fxbuf,
 	return true;
 }
 
-/*
- * Update the value of PKRU register that was already pushed onto the signal frame.
- */
-static inline int update_pkru_in_sigframe(struct xregs_state __user *buf, u32 pkru)
-{
-	if (unlikely(!cpu_feature_enabled(X86_FEATURE_OSPKE)))
-		return 0;
-	return __put_user(pkru, (unsigned int __user *)get_xsave_addr_user(buf, XFEATURE_PKRU));
-}
-
 /*
  * Signal frame handlers.
  */
@@ -168,14 +158,8 @@ static inline bool save_xstate_epilog(void __user *buf, int ia32_frame,
 
 static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf, u32 pkru)
 {
-	int err = 0;
-
-	if (use_xsave()) {
-		err = xsave_to_user_sigframe(buf);
-		if (!err)
-			err = update_pkru_in_sigframe(buf, pkru);
-		return err;
-	}
+	if (use_xsave())
+		return xsave_to_user_sigframe(buf, pkru);
 
 	if (use_fxsr())
 		return fxsave_to_user_sigframe((struct fxregs_state __user *) buf);
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 0b86a5002c84..6b2924fbe5b8 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -69,6 +69,16 @@ static inline u64 xfeatures_mask_independent(void)
 	return fpu_kernel_cfg.independent_features;
 }
 
+/*
+ * Update the value of PKRU register that was already pushed onto the signal frame.
+ */
+static inline int update_pkru_in_sigframe(struct xregs_state __user *buf, u32 pkru)
+{
+	if (unlikely(!cpu_feature_enabled(X86_FEATURE_OSPKE)))
+		return 0;
+	return __put_user(pkru, (unsigned int __user *)get_xsave_addr_user(buf, XFEATURE_PKRU));
+}
+
 /* XSAVE/XRSTOR wrapper functions */
 
 #ifdef CONFIG_X86_64
@@ -256,7 +266,7 @@ static inline u64 xfeatures_need_sigframe_write(void)
  * The caller has to zero buf::header before calling this because XSAVE*
  * does not touch the reserved fields in the header.
  */
-static inline int xsave_to_user_sigframe(struct xregs_state __user *buf)
+static inline int xsave_to_user_sigframe(struct xregs_state __user *buf, u32 pkru)
 {
 	/*
 	 * Include the features which are not xsaved/rstored by the kernel
@@ -281,6 +291,9 @@ static inline int xsave_to_user_sigframe(struct xregs_state __user *buf)
 	XSTATE_OP(XSAVE, buf, lmask, hmask, err);
 	clac();
 
+	if (!err)
+		err = update_pkru_in_sigframe(buf, pkru);
+
 	return err;
 }
 
-- 
2.43.5