linux-kernel - [PATCH v3 2/2] x86/pkeys: Set XSTATE_BV[PKRU] to 1 so that PKRU is XRSTOR'd correctly

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Message-ID: <20241119174520.3987538-3-aruna.ramakrishna@oracle.com>
Date: Tue, 19 Nov 2024 17:45:20 +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,
        aruna.ramakrishna@...cle.com
Subject: [PATCH v3 2/2] x86/pkeys: Set XSTATE_BV[PKRU] to 1 so that PKRU is XRSTOR'd correctly

PKRU value is not XRSTOR'd from the XSAVE area if the corresponding
XSTATE_BV[i] bit is 0. A wrpkru(0) sets XSTATE_BV[PKRU] to 0 on AMD
systems, which means the PKRU value updated on the sigframe later on,
in update_pkru_in_sigframe(), is ignored.

To make this behavior consistent across Intel and AMD systems, and to
ensure that the PKRU value updated on the sigframe is always restored
correctly, explicitly set XSTATE_BV[PKRU] to 1.

Fixes: 70044df250d0 ("x86/pkeys: Update PKRU to enable all pkeys before XSAVE")

Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
Suggested-by: Rudi Horn <rudi.horn@...cle.com>
---
 arch/x86/kernel/fpu/xstate.h | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 6b2924fbe5b8..aa16f1a1bbcf 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -72,10 +72,22 @@ static inline u64 xfeatures_mask_independent(void)
 /*
  * 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)
+static inline int update_pkru_in_sigframe(struct xregs_state __user *buf, u64 mask, u32 pkru)
 {
+	u64 xstate_bv;
+	int err;
+
 	if (unlikely(!cpu_feature_enabled(X86_FEATURE_OSPKE)))
 		return 0;
+
+	/* Mark PKRU as in-use so that it is restored correctly. */
+	xstate_bv = (mask & xfeatures_in_use()) | XFEATURE_MASK_PKRU;
+
+	err =  __put_user(xstate_bv, &buf->header.xfeatures);
+	if (err)
+		return err;
+
+	/* Update PKRU value in the userspace xsave buffer. */
 	return __put_user(pkru, (unsigned int __user *)get_xsave_addr_user(buf, XFEATURE_PKRU));
 }
 
@@ -292,7 +304,7 @@ static inline int xsave_to_user_sigframe(struct xregs_state __user *buf, u32 pkr
 	clac();
 
 	if (!err)
-		err = update_pkru_in_sigframe(buf, pkru);
+		err = update_pkru_in_sigframe(buf, mask, pkru);
 
 	return err;
 }
-- 
2.43.5