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Message-Id: <20170410164420.64003-4-thgarnie@google.com>
Date: Mon, 10 Apr 2017 09:44:20 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Arnd Bergmann <arnd@...db.de>,
Dave Hansen <dave.hansen@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Garnier <thgarnie@...gle.com>,
David Howells <dhowells@...hat.com>,
René Nyffenegger <mail@...enyffenegger.ch>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Oleg Nesterov <oleg@...hat.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Kees Cook <keescook@...omium.org>,
Rik van Riel <riel@...hat.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Brian Gerst <brgerst@...il.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Russell King <linux@...linux.org.uk>,
Will Deacon <will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>,
Mark Rutland <mark.rutland@....com>,
James Morse <james.morse@....com>
Cc: linux-s390@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-api@...r.kernel.org,
x86@...nel.org,
linux-arm-kernel@...ts.infradead.org,
kernel-hardening@...ts.openwall.com
Subject: [PATCH v7 4/4] arm64/syscalls: Architecture specific pre-usermode check
Disable the generic pre-usermode check in favor of an optimized
implementation. This patch adds specific checks on user-mode return path
to make it faster and smaller.
The address limit is checked on each syscall return path to user-mode.
If it was changed, a generic handler is called to stop the kernel on an
explicit check.
Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
Based on next-20170410
---
arch/arm64/Kconfig | 1 +
arch/arm64/kernel/entry.S | 13 +++++++++++++
2 files changed, 14 insertions(+)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 9b8fcab7da56..3f9e8e7d9376 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -24,6 +24,7 @@ config ARM64
select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
select ARCH_WANT_FRAME_POINTERS
select ARCH_HAS_UBSAN_SANITIZE_ALL
+ select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
select ARM_AMBA
select ARM_ARCH_TIMER
select ARM_GIC
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 43512d4d7df2..bdd094c7837a 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -744,6 +744,8 @@ ENDPROC(cpu_switch_to)
ret_fast_syscall:
disable_irq // disable interrupts
str x0, [sp, #S_X0] // returned x0
+ ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change
+ tbnz x2, #63, addr_limit_fail
ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing
and x2, x1, #_TIF_SYSCALL_WORK
cbnz x2, ret_fast_syscall_trace
@@ -771,6 +773,9 @@ work_pending:
*/
ret_to_user:
disable_irq // disable interrupts
+ ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change
+ tbnz x2, #63, addr_limit_fail
+
ldr x1, [tsk, #TSK_TI_FLAGS]
and x2, x1, #_TIF_WORK_MASK
cbnz x2, work_pending
@@ -780,6 +785,14 @@ finish_ret_to_user:
ENDPROC(ret_to_user)
/*
+ * Address limit was incorrect before returning in user-mode which could be
+ * used to elevate privileges. Call the generic handler to stop the kernel on
+ * the appropriate check. This function does not return.
+ */
+addr_limit_fail:
+ bl address_limit_check_failed
+
+/*
* This is how we return from a fork.
*/
ENTRY(ret_from_fork)
--
2.12.2.715.g7642488e1d-goog
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