linux-kernel - [PATCH v3 2/4] x86/pkeys: Add helper functions to update PKRU on sigframe

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Message-Id: <20240425180542.1042933-3-aruna.ramakrishna@oracle.com>
Date: Thu, 25 Apr 2024 18:05:40 +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, keith.lucas@...cle.com, aruna.ramakrishna@...cle.com
Subject: [PATCH v3 2/4] x86/pkeys: Add helper functions to update PKRU on sigframe

This patch adds helper functions that will update PKRU value on the
sigframe after XSAVE.

These functions will be called in a later patch; this patch does not
change any behavior as yet.

Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
---
 arch/x86/kernel/fpu/signal.c | 26 ++++++++++++++++++++++++++
 arch/x86/kernel/fpu/xstate.c | 13 +++++++++++++
 arch/x86/kernel/fpu/xstate.h |  1 +
 arch/x86/kernel/signal.c     | 12 ++++++++++++
 4 files changed, 52 insertions(+)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 7654f368accd..dce84cce7cf8 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -63,6 +63,32 @@ 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)
+{
+	int err = -EFAULT;
+	struct _fpx_sw_bytes fx_sw;
+	struct pkru_state *pk = NULL;
+
+	if (unlikely(!check_xstate_in_sigframe((void __user *) buf, &fx_sw)))
+		goto out;
+
+	pk = get_xsave_addr_user(buf, XFEATURE_PKRU);
+	if (!pk || !user_write_access_begin(buf, sizeof(struct xregs_state)))
+		goto out;
+	unsafe_put_user(pkru, (unsigned int __user *) pk, uaccess_end);
+
+	err = 0;
+uaccess_end:
+	user_access_end();
+out:
+	return err;
+}
+
 /*
  * Signal frame handlers.
  */
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 33a214b1a4ce..8395a3633709 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -992,6 +992,19 @@ void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr)
 	return __raw_xsave_addr(xsave, xfeature_nr);
 }
 
+/*
+ * Given an xstate feature nr, calculate where in the xsave
+ * buffer the state is. The xsave buffer should be in standard
+ * format, not compacted (e.g. user mode signal frames).
+ */
+void *get_xsave_addr_user(struct xregs_state __user *xsave, int xfeature_nr)
+{
+	if (WARN_ON_ONCE(!xfeature_enabled(xfeature_nr)))
+		return NULL;
+
+	return (void *)xsave + xstate_offsets[xfeature_nr];
+}
+
 #ifdef CONFIG_ARCH_HAS_PKEYS
 
 /*
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 19ca623ffa2a..6511797940ad 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -55,6 +55,7 @@ extern void fpu__init_cpu_xstate(void);
 extern void fpu__init_system_xstate(unsigned int legacy_size);
 
 extern void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr);
+extern void *get_xsave_addr_user(struct xregs_state *xsave, int xfeature_nr);
 
 static inline u64 xfeatures_mask_supervisor(void)
 {
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index d1c84b7f6852..75dfd05c59aa 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -225,6 +225,18 @@ setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs, u32 pkru)
 	}
 }
 
+/*
+ * Enable all pkeys to ensure that both the current stack and the alternate
+ * signal stack are always writeable.
+ */
+static inline u32 sig_prepare_pkru(void)
+{
+	u32 orig_pkru = read_pkru();
+
+	write_pkru(0);
+	return orig_pkru;
+}
+
 static void
 handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 {
-- 
2.39.3