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arm64: VHE: Enable EL2 MMU from the idmap

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Enabling the MMU requires the write to SCTLR_ELx (and the ISB
that follows) to live in some identity-mapped memory. Otherwise,
the translation will result in something totally unexpected
(either fetching the wrong instruction stream, or taking a
fault of some sort).

This is exactly what happens in mutate_to_vhe(), as this code
lives in the .hyp.text section, which isn't identity-mapped.
With the right configuration, this explodes badly.

Extract the MMU-enabling part of mutate_to_vhe(), and move
it to its own function that lives in the idmap. This ensures
nothing bad happens.

Fixes: f359182291 ("arm64: Provide an 'upgrade to VHE' stub hypercall")
Reported-by: "kernelci.org bot" <bot@kernelci.org>
Tested-by: Guillaume Tucker <guillaume.tucker@collabora.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210224093738.3629662-2-maz@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Marc Zyngier 2021-02-24 09:37:36 +00:00 committed by Will Deacon
parent 610e4dc8ac
commit f1b6cff7c9
1 changed files with 26 additions and 13 deletions
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39
arch/arm64/kernel/hyp-stub.S
View file

@ -75,9 +75,6 @@ SYM_CODE_END(el1_sync)
// nVHE? No way! Give me the real thing!
SYM_CODE_START_LOCAL(mutate_to_vhe)
// Be prepared to fail
mov_q x0, HVC_STUB_ERR
// Sanity check: MMU *must* be off
mrs x1, sctlr_el2
tbnz x1, #0, 1f
@ -96,8 +93,11 @@ SYM_CODE_START_LOCAL(mutate_to_vhe)
cmp x1, xzr
and x2, x2, x1
csinv x2, x2, xzr, ne
cbz x2, 1f
cbnz x2, 2f
1: mov_q x0, HVC_STUB_ERR
eret
2:
// Engage the VHE magic!
mov_q x0, HCR_HOST_VHE_FLAGS
msr hcr_el2, x0
@ -131,6 +131,24 @@ SYM_CODE_START_LOCAL(mutate_to_vhe)
msr mair_el1, x0
isb
// Hack the exception return to stay at EL2
mrs x0, spsr_el1
and x0, x0, #~PSR_MODE_MASK
mov x1, #PSR_MODE_EL2h
orr x0, x0, x1
msr spsr_el1, x0
b enter_vhe
SYM_CODE_END(mutate_to_vhe)
// At the point where we reach enter_vhe(), we run with
// the MMU off (which is enforced by mutate_to_vhe()).
// We thus need to be in the idmap, or everything will
// explode when enabling the MMU.
.pushsection .idmap.text, "ax"
SYM_CODE_START_LOCAL(enter_vhe)
// Invalidate TLBs before enabling the MMU
tlbi vmalle1
dsb nsh
@ -143,17 +161,12 @@ SYM_CODE_START_LOCAL(mutate_to_vhe)
mov_q x0, INIT_SCTLR_EL1_MMU_OFF
msr_s SYS_SCTLR_EL12, x0
// Hack the exception return to stay at EL2
mrs x0, spsr_el1
and x0, x0, #~PSR_MODE_MASK
mov x1, #PSR_MODE_EL2h
orr x0, x0, x1
msr spsr_el1, x0
mov x0, xzr
1: eret
SYM_CODE_END(mutate_to_vhe)
eret
SYM_CODE_END(enter_vhe)
.popsection
.macro invalid_vector label
SYM_CODE_START_LOCAL(\label)