diff options
| author | Dimitris Papastamos <dimitris.papastamos@arm.com> | 2017-12-18 13:46:21 +0000 |
|---|---|---|
| committer | Dimitris Papastamos <dimitris.papastamos@arm.com> | 2018-01-11 10:26:15 +0000 |
| commit | a1781a211a53df6a24345d774c0f2eaa5b675ca8 (patch) | |
| tree | 134af9ccff89ab1d2ddac0624d80bb1c18349646 /bl31/bl31.mk | |
| parent | f62ad322695d16178db464dc062fe0af592c6780 (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/bl31.mk')
| -rw-r--r-- | bl31/bl31.mk | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/bl31/bl31.mk b/bl31/bl31.mk index 0732e052..8ff8f89b 100644 --- a/bl31/bl31.mk +++ b/bl31/bl31.mk @@ -59,7 +59,8 @@ BL31_SOURCES += lib/extensions/sve/sve.c endif 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 endif BL31_LINKERFILE := bl31/bl31.ld.S |