Prevent speculative execution past ERET
Even though ERET always causes a jump to another address, aarch64 CPUs
speculatively execute following instructions as if the ERET
instruction was not a jump instruction.
The speculative execution does not cross privilege-levels (to the jump
target as one would expect), but it continues on the kernel privilege
level as if the ERET instruction did not change the control flow -
thus execution anything that is accidentally linked after the ERET
instruction. Later, the results of this speculative execution are
always architecturally discarded, however they can leak data using
microarchitectural side channels. This speculative execution is very
reliable (seems to be unconditional) and it manages to complete even
relatively performance-heavy operations (e.g. multiple dependent
fetches from uncached memory).
This was fixed in Linux, FreeBSD, OpenBSD and Optee OS:
https://github.com/torvalds/linux/commit/679db70801da9fda91d26caf13bf5b5ccc74e8e8
https://github.com/freebsd/freebsd/commit/29fb48ace4186a41c409fde52bcf4216e9e50b61
https://github.com/openbsd/src/commit/3a08873ece1cb28ace89fd65e8f3c1375cc98de2
https://github.com/OP-TEE/optee_os/commit/abfd092aa19f9c0251e3d5551e2d68a9ebcfec8a
It is demonstrated in a SafeSide example:
https://github.com/google/safeside/blob/master/demos/eret_hvc_smc_wrapper.cc
https://github.com/google/safeside/blob/master/kernel_modules/kmod_eret_hvc_smc/eret_hvc_smc_module.c
Signed-off-by: Anthony Steinhauser <asteinhauser@google.com>
Change-Id: Iead39b0b9fb4b8d8b5609daaa8be81497ba63a0f
diff --git a/lib/cpus/aarch64/cortex_a76.S b/lib/cpus/aarch64/cortex_a76.S
index 868667e..baefa46 100644
--- a/lib/cpus/aarch64/cortex_a76.S
+++ b/lib/cpus/aarch64/cortex_a76.S
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2020, ARM Limited and Contributors. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
@@ -85,7 +85,7 @@
bic x3, x2, #CORTEX_A76_CPUACTLR2_EL1_DISABLE_LOAD_PASS_STORE
csel x3, x3, x1, eq
msr CORTEX_A76_CPUACTLR2_EL1, x3
- eret /* ERET implies ISB */
+ exception_return /* exception_return contains ISB */
.endif
1:
/*
diff --git a/lib/cpus/aarch64/neoverse_n1.S b/lib/cpus/aarch64/neoverse_n1.S
index faf53a8..d058d98 100644
--- a/lib/cpus/aarch64/neoverse_n1.S
+++ b/lib/cpus/aarch64/neoverse_n1.S
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2020, ARM Limited and Contributors. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
@@ -553,7 +553,7 @@
*/
esb
#endif
- eret
+ exception_return
1:
ret
endfunc neoverse_n1_errata_ic_trap_handler
diff --git a/lib/cpus/aarch64/wa_cve_2017_5715_mmu.S b/lib/cpus/aarch64/wa_cve_2017_5715_mmu.S
index 9277cc6..5134ee3 100644
--- a/lib/cpus/aarch64/wa_cve_2017_5715_mmu.S
+++ b/lib/cpus/aarch64/wa_cve_2017_5715_mmu.S
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2020, ARM Limited and Contributors. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
@@ -48,7 +48,7 @@
ccmp w0, w1, #0, eq
/* Static predictor will predict a fall through */
bne 1f
- eret
+ exception_return
1:
.endif
diff --git a/lib/el3_runtime/aarch64/context.S b/lib/el3_runtime/aarch64/context.S
index 1bbd610..9bd25ba 100644
--- a/lib/el3_runtime/aarch64/context.S
+++ b/lib/el3_runtime/aarch64/context.S
@@ -534,6 +534,6 @@
*/
esb
#endif
- eret
+ exception_return
endfunc el3_exit