linux-kernel - [RFC 2/6] x86/vdso: add mask and flags to extable

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Date:   Wed, 24 Feb 2021 23:29:06 -0800
From:   Nadav Amit <nadav.amit@...il.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Hugh Dickins <hughd@...gle.com>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Nadav Amit <namit@...are.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org
Subject: [RFC 2/6] x86/vdso: add mask and flags to extable

From: Nadav Amit <namit@...are.com>

Add a "mask" field to vDSO exception tables that says which exceptions
should be handled.

Add a "flags" field to vDSO as well to provide additional information
about the exception.

The existing preprocessor macro _ASM_VDSO_EXTABLE_HANDLE for assembly is
not easy to use as it requires the user to stringify the expanded C
macro. Remove _ASM_VDSO_EXTABLE_HANDLE and use a similar scheme to
ALTERNATIVE, using assembly macros directly in assembly without wrapping
them in C macros.

Move the vsgx supported exceptions test out of the generic C code into
vsgx-specific assembly by setting vsgx supported exceptions in the mask.

Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: x86@...nel.org
Signed-off-by: Nadav Amit <namit@...are.com>
---
 arch/x86/entry/vdso/extable.c |  9 +--------
 arch/x86/entry/vdso/extable.h | 21 +++++++++++++--------
 arch/x86/entry/vdso/vsgx.S    |  9 +++++++--
 3 files changed, 21 insertions(+), 18 deletions(-)

diff --git a/arch/x86/entry/vdso/extable.c b/arch/x86/entry/vdso/extable.c
index c81e78636220..93fb37bd32ad 100644
--- a/arch/x86/entry/vdso/extable.c
+++ b/arch/x86/entry/vdso/extable.c
@@ -7,6 +7,7 @@
 
 struct vdso_exception_table_entry {
 	int insn, fixup;
+	unsigned int mask, flags;
 };
 
 bool fixup_vdso_exception(struct pt_regs *regs, int trapnr,
@@ -17,14 +18,6 @@ bool fixup_vdso_exception(struct pt_regs *regs, int trapnr,
 	unsigned int nr_entries, i;
 	unsigned long base;
 
-	/*
-	 * Do not attempt to fixup #DB or #BP.  It's impossible to identify
-	 * whether or not a #DB/#BP originated from within an SGX enclave and
-	 * SGX enclaves are currently the only use case for vDSO fixup.
-	 */
-	if (trapnr == X86_TRAP_DB || trapnr == X86_TRAP_BP)
-		return false;
-
 	if (!current->mm->context.vdso)
 		return false;
 
diff --git a/arch/x86/entry/vdso/extable.h b/arch/x86/entry/vdso/extable.h
index b56f6b012941..7ca8a0776805 100644
--- a/arch/x86/entry/vdso/extable.h
+++ b/arch/x86/entry/vdso/extable.h
@@ -2,26 +2,31 @@
 #ifndef __VDSO_EXTABLE_H
 #define __VDSO_EXTABLE_H
 
+#include <asm/trapnr.h>
+
+#define ASM_VDSO_ASYNC_FLAGS	(1 << 0)
+
 /*
  * Inject exception fixup for vDSO code.  Unlike normal exception fixup,
  * vDSO uses a dedicated handler the addresses are relative to the overall
  * exception table, not each individual entry.
  */
 #ifdef __ASSEMBLY__
-#define _ASM_VDSO_EXTABLE_HANDLE(from, to)	\
-	ASM_VDSO_EXTABLE_HANDLE from to
-
-.macro ASM_VDSO_EXTABLE_HANDLE from:req to:req
+.macro ASM_VDSO_EXTABLE_HANDLE from:req to:req mask:req flags:req
 	.pushsection __ex_table, "a"
 	.long (\from) - __ex_table
 	.long (\to) - __ex_table
+	.long (\mask)
+	.long (\flags)
 	.popsection
 .endm
 #else
-#define _ASM_VDSO_EXTABLE_HANDLE(from, to)	\
-	".pushsection __ex_table, \"a\"\n"      \
-	".long (" #from ") - __ex_table\n"      \
-	".long (" #to ") - __ex_table\n"        \
+#define ASM_VDSO_EXTABLE_HANDLE(from, to, mask, flags)		\
+	".pushsection __ex_table, \"a\"\n"			\
+	".long (" #from ") - __ex_table\n"			\
+	".long (" #to ") - __ex_table\n"			\
+	".long (" #mask ")\n"					\
+	".long (" #flags ")\n"					\
 	".popsection\n"
 #endif
 
diff --git a/arch/x86/entry/vdso/vsgx.S b/arch/x86/entry/vdso/vsgx.S
index 86a0e94f68df..c588255af480 100644
--- a/arch/x86/entry/vdso/vsgx.S
+++ b/arch/x86/entry/vdso/vsgx.S
@@ -4,6 +4,7 @@
 #include <asm/export.h>
 #include <asm/errno.h>
 #include <asm/enclu.h>
+#include <asm/trapnr.h>
 
 #include "extable.h"
 
@@ -146,6 +147,10 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
 
 	.cfi_endproc
 
-_ASM_VDSO_EXTABLE_HANDLE(.Lenclu_eenter_eresume, .Lhandle_exception)
-
+/*
+ * Do not attempt to fixup #DB or #BP.  It's impossible to identify
+ * whether or not a #DB/#BP originated from within an SGX enclave.
+ */
+ASM_VDSO_EXTABLE_HANDLE .Lenclu_eenter_eresume, .Lhandle_exception,	\
+			~((1<<X86_TRAP_DB)+(1<<X86_TRAP_BP)), 0
 SYM_FUNC_END(__vdso_sgx_enter_enclave)
-- 
2.25.1