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    Subject[PATCH 5.16 26/53] arm64: entry: Make the kpti trampolines kpti sequence optional
    Date
    From: James Morse <james.morse@arm.com>

    commit c47e4d04ba0f1ea17353d85d45f611277507e07a upstream.

    Spectre-BHB needs to add sequences to the vectors. Having one global
    set of vectors is a problem for big/little systems where the sequence
    is costly on cpus that are not vulnerable.

    Making the vectors per-cpu in the style of KVM's bh_harden_hyp_vecs
    requires the vectors to be generated by macros.

    Make the kpti re-mapping of the kernel optional, so the macros can be
    used without kpti.

    Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
    Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: James Morse <james.morse@arm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/arm64/kernel/entry.S | 18 ++++++++++++------
    1 file changed, 12 insertions(+), 6 deletions(-)

    --- a/arch/arm64/kernel/entry.S
    +++ b/arch/arm64/kernel/entry.S
    @@ -646,9 +646,10 @@ alternative_else_nop_endif
    sub \dst, \dst, PAGE_SIZE
    .endm

    - .macro tramp_ventry, vector_start, regsize
    + .macro tramp_ventry, vector_start, regsize, kpti
    .align 7
    1:
    + .if \kpti == 1
    .if \regsize == 64
    msr tpidrro_el0, x30 // Restored in kernel_ventry
    .endif
    @@ -671,9 +672,14 @@ alternative_insn isb, nop, ARM64_WORKARO
    alternative_if_not ARM64_WORKAROUND_CAVIUM_TX2_219_PRFM
    prfm plil1strm, [x30, #(1b - \vector_start)]
    alternative_else_nop_endif
    +
    msr vbar_el1, x30
    - add x30, x30, #(1b - \vector_start + 4)
    isb
    + .else
    + ldr x30, =vectors
    + .endif // \kpti == 1
    +
    + add x30, x30, #(1b - \vector_start + 4)
    ret
    .org 1b + 128 // Did we overflow the ventry slot?
    .endm
    @@ -691,15 +697,15 @@ alternative_else_nop_endif
    sb
    .endm

    - .macro generate_tramp_vector
    + .macro generate_tramp_vector, kpti
    .Lvector_start\@:
    .space 0x400

    .rept 4
    - tramp_ventry .Lvector_start\@, 64
    + tramp_ventry .Lvector_start\@, 64, \kpti
    .endr
    .rept 4
    - tramp_ventry .Lvector_start\@, 32
    + tramp_ventry .Lvector_start\@, 32, \kpti
    .endr
    .endm

    @@ -710,7 +716,7 @@ alternative_else_nop_endif
    .pushsection ".entry.tramp.text", "ax"
    .align 11
    SYM_CODE_START_NOALIGN(tramp_vectors)
    - generate_tramp_vector
    + generate_tramp_vector kpti=1
    SYM_CODE_END(tramp_vectors)

    SYM_CODE_START(tramp_exit_native)

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