path: root/bl31
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authorDimitris Papastamos <dimitris.papastamos@arm.com>2017-12-18 13:46:21 +0000
committerDimitris Papastamos <dimitris.papastamos@arm.com>2018-01-11 10:26:15 +0000
commita1781a211a53df6a24345d774c0f2eaa5b675ca8 (patch)
tree134af9ccff89ab1d2ddac0624d80bb1c18349646 /bl31
parentf62ad322695d16178db464dc062fe0af592c6780 (diff)
Workaround for CVE-2017-5715 on Cortex A73 and A75
Invalidate the Branch Target Buffer (BTB) on entry to EL3 by temporarily dropping into AArch32 Secure-EL1 and executing the `BPIALL` instruction. This is achieved by using 3 vector tables. There is the runtime vector table which is used to handle exceptions and 2 additional tables which are required to implement this workaround. The additional tables are `vbar0` and `vbar1`. The sequence of events for handling a single exception is as follows: 1) Install vector table `vbar0` which saves the CPU context on entry to EL3 and sets up the Secure-EL1 context to execute in AArch32 mode with the MMU disabled and I$ enabled. This is the default vector table. 2) Before doing an ERET into Secure-EL1, switch vbar to point to another vector table `vbar1`. This is required to restore EL3 state when returning from the workaround, before proceeding with normal EL3 exception handling. 3) While in Secure-EL1, the `BPIALL` instruction is executed and an SMC call back to EL3 is performed. 4) On entry to EL3 from Secure-EL1, the saved context from step 1) is restored. The vbar is switched to point to `vbar0` in preparation to handle further exceptions. Finally a branch to the runtime vector table entry is taken to complete the handling of the original exception. This workaround is enabled by default on the affected CPUs. NOTE ==== There are 4 different stubs in Secure-EL1. Each stub corresponds to an exception type such as Sync/IRQ/FIQ/SError. Each stub will move a different value in `R0` before doing an SMC call back into EL3. Without this piece of information it would not be possible to know what the original exception type was as we cannot use `ESR_EL3` to distinguish between IRQs and FIQs. Change-Id: I90b32d14a3735290b48685d43c70c99daaa4b434 Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>
Diffstat (limited to 'bl31')
1 files changed, 2 insertions, 1 deletions
diff --git a/bl31/bl31.mk b/bl31/bl31.mk
index 0732e05215..8ff8f89bb8 100644
--- a/bl31/bl31.mk
+++ b/bl31/bl31.mk
@@ -59,7 +59,8 @@ BL31_SOURCES += lib/extensions/sve/sve.c
ifeq (${WORKAROUND_CVE_2017_5715},1)
-BL31_SOURCES += lib/cpus/aarch64/workaround_cve_2017_5715_mmu.S
+BL31_SOURCES += lib/cpus/aarch64/workaround_cve_2017_5715_mmu.S \
+ lib/cpus/aarch64/workaround_cve_2017_5715_bpiall.S
BL31_LINKERFILE := bl31/bl31.ld.S