linux-kernel - [PATCH 2/2] x86/xen/64: Rearrange the SYSCALL entries

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-Id: <14fee348e3e86c994400d68085217d1232a637d6.1437951794.git.luto@kernel.org>
Date:	Sun, 26 Jul 2015 16:29:10 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	X86 ML <x86@...nel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	Andrew Cooper <andrew.cooper3@...rix.com>
Cc:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 2/2] x86/xen/64: Rearrange the SYSCALL entries

Xen's raw SYSCALL entries are much less weird than native.  Rather
than fudging them to look like native entries, use the Xen-provided
stack frame directly.

This lets us eliminate entry_SYSCALL_64_after_swapgs and two uses
of the SWAPGS_UNSAFE_STACK paravirt hook.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/entry/entry_64.S        |  9 +--------
 arch/x86/entry/entry_64_compat.S |  2 +-
 arch/x86/xen/xen-asm_64.S        | 24 ++++++++++--------------
 3 files changed, 12 insertions(+), 23 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f47996910331..ebe7e2ca19fe 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -134,14 +134,7 @@ ENTRY(entry_SYSCALL_64)
 	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
 	 * it is too small to ever cause noticeable irq latency.
 	 */
-	SWAPGS_UNSAFE_STACK
-	/*
-	 * A hypervisor implementation might want to use a label
-	 * after the swapgs, so that it can do the swapgs
-	 * for the guest and jump here on syscall.
-	 */
-GLOBAL(entry_SYSCALL_64_after_swapgs)
-
+	swapgs
 	movq	%rsp, PER_CPU_VAR(rsp_scratch)
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index d39495d6446e..beae2b75b588 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -309,7 +309,7 @@ ENTRY(entry_SYSCALL_compat)
 	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
 	 * it is too small to ever cause noticeable irq latency.
 	 */
-	SWAPGS_UNSAFE_STACK
+	swapgs
 	movl	%esp, %r8d
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 
diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index f22667abf7b9..c2b5868a9967 100644
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -100,34 +100,30 @@ RELOC(xen_sysret32, 1b+1)
  *	rip
  *	r11
  * rsp->rcx
- *
- * In all the entrypoints, we undo all that to make it look like a
- * CPU-generated syscall/sysenter and jump to the normal entrypoint.
  */
 
-.macro undo_xen_syscall
-	mov 0*8(%rsp), %rcx
-	mov 1*8(%rsp), %r11
-	mov 5*8(%rsp), %rsp
-.endm
-
 /* Normal 64-bit system call target */
 ENTRY(xen_syscall_target)
-	undo_xen_syscall
-	jmp entry_SYSCALL_64_after_swapgs
+	popq %rcx
+	popq %r11
+	jmp entry_SYSCALL_64_after_hwframe
 ENDPROC(xen_syscall_target)
 
 #ifdef CONFIG_IA32_EMULATION
 
 /* 32-bit compat syscall target */
 ENTRY(xen_syscall32_target)
-	undo_xen_syscall
-	jmp entry_SYSCALL_compat
+	popq %rcx
+	popq %r11
+	movl (3*8)(%rsp), %r8d		/* r8d = user esp */
+	jmp entry_SYSCALL_compat_after_hwframe_esp_in_r8d
 ENDPROC(xen_syscall32_target)
 
 /* 32-bit compat sysenter target */
 ENTRY(xen_sysenter_target)
-	undo_xen_syscall
+	mov 0*8(%rsp), %rcx
+	mov 1*8(%rsp), %r11
+	mov 5*8(%rsp), %rsp
 	jmp entry_SYSENTER_compat
 ENDPROC(xen_sysenter_target)
 
-- 
2.4.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/