linux-kernel - [RFC PATCH 03/13] powerpc/dexcr: Handle hashchk exception

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Date:   Mon, 28 Nov 2022 13:44:48 +1100
From:   Benjamin Gray <bgray@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     ajd@...ux.ibm.com, ruscur@...sell.cc, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org, cmr@...escreens.de,
        Benjamin Gray <bgray@...ux.ibm.com>
Subject: [RFC PATCH 03/13] powerpc/dexcr: Handle hashchk exception

Recognise and pass the appropriate signal to the user program when a
hashchk instruction triggers. This is independent of allowing
configuration of DEXCR[NPHIE], as a hypervisor can enforce this aspect
regardless of the kernel.

Signed-off-by: Benjamin Gray <bgray@...ux.ibm.com>
---
 arch/powerpc/include/asm/ppc-opcode.h |  1 +
 arch/powerpc/include/asm/processor.h  |  6 ++++++
 arch/powerpc/kernel/dexcr.c           | 22 ++++++++++++++++++++++
 arch/powerpc/kernel/traps.c           |  6 ++++++
 4 files changed, 35 insertions(+)

diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
index 21e33e46f4b8..89b316466ed1 100644
--- a/arch/powerpc/include/asm/ppc-opcode.h
+++ b/arch/powerpc/include/asm/ppc-opcode.h
@@ -215,6 +215,7 @@
 #define OP_31_XOP_STFSX	    663
 #define OP_31_XOP_STFSUX    695
 #define OP_31_XOP_STFDX     727
+#define OP_31_XOP_HASHCHK   754
 #define OP_31_XOP_STFDUX    759
 #define OP_31_XOP_LHBRX     790
 #define OP_31_XOP_LFIWAX    855
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 0a8a793b8b8b..c17ec1e44c86 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -448,10 +448,16 @@ void *exit_vmx_ops(void *dest);
 
 #ifdef CONFIG_PPC_BOOK3S_64
 
+bool is_hashchk_trap(struct pt_regs const *regs);
 unsigned long get_thread_dexcr(struct thread_struct const *t);
 
 #else
 
+static inline bool is_hashchk_trap(struct pt_regs const *regs)
+{
+	return false;
+}
+
 static inline unsigned long get_thread_dexcr(struct thread_struct const *t)
 {
 	return 0;
diff --git a/arch/powerpc/kernel/dexcr.c b/arch/powerpc/kernel/dexcr.c
index 32a0a69ff638..11515e67afac 100644
--- a/arch/powerpc/kernel/dexcr.c
+++ b/arch/powerpc/kernel/dexcr.c
@@ -3,6 +3,9 @@
 
 #include <asm/cpu_has_feature.h>
 #include <asm/cputable.h>
+#include <asm/disassemble.h>
+#include <asm/inst.h>
+#include <asm/ppc-opcode.h>
 #include <asm/processor.h>
 #include <asm/reg.h>
 
@@ -19,6 +22,25 @@ static int __init dexcr_init(void)
 }
 early_initcall(dexcr_init);
 
+bool is_hashchk_trap(struct pt_regs const *regs)
+{
+	ppc_inst_t insn;
+
+	if (!cpu_has_feature(CPU_FTR_DEXCR_NPHIE))
+		return false;
+
+	if (get_user_instr(insn, (void __user *)regs->nip)) {
+		WARN_ON(1);
+		return false;
+	}
+
+	if (ppc_inst_primary_opcode(insn) == 31 &&
+	    get_xop(ppc_inst_val(insn)) == OP_31_XOP_HASHCHK)
+		return true;
+
+	return false;
+}
+
 unsigned long get_thread_dexcr(struct thread_struct const *t)
 {
 	return DEFAULT_DEXCR;
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 9bdd79aa51cf..b83f5b382f24 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1516,6 +1516,12 @@ static void do_program_check(struct pt_regs *regs)
 				return;
 			}
 		}
+
+		if (user_mode(regs) && is_hashchk_trap(regs)) {
+			_exception(SIGILL, regs, ILL_ILLOPN, regs->nip);
+			return;
+		}
+
 		_exception(SIGTRAP, regs, TRAP_BRKPT, regs->nip);
 		return;
 	}
-- 
2.38.1