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Date: Fri, 18 Oct 2019 09:43:20 -0700
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.org>, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Dave Martin <Dave.Martin@....com>, Kees Cook <keescook@...omium.org>,
Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>,
clang-built-linux <clang-built-linux@...glegroups.com>, kernel-hardening@...ts.openwall.com,
Linux ARM <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/18] arm64: mm: don't use x18 in idmap_kpti_install_ng_mappings
On Fri, Oct 18, 2019 at 9:10 AM Sami Tolvanen <samitolvanen@...gle.com> wrote:
>
> idmap_kpti_install_ng_mappings uses x18 as a temporary register, which
> will result in a conflict when x18 is reserved. Use x16 and x17 instead
> where needed.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
TIL about .req/.unreq. Seems like a nice way of marking "variable"
lifetime. Technically, only `pte` needed to be moved to reuse
{w|x}16, but moving most the unreqs together is nicer than splitting
them apart. The usage all looks correct to me.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
> arch/arm64/mm/proc.S | 63 ++++++++++++++++++++++----------------------
> 1 file changed, 32 insertions(+), 31 deletions(-)
>
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index a1e0592d1fbc..fdabf40a83c8 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -250,15 +250,15 @@ ENTRY(idmap_kpti_install_ng_mappings)
> /* We're the boot CPU. Wait for the others to catch up */
> sevl
> 1: wfe
> - ldaxr w18, [flag_ptr]
> - eor w18, w18, num_cpus
> - cbnz w18, 1b
> + ldaxr w17, [flag_ptr]
> + eor w17, w17, num_cpus
> + cbnz w17, 1b
>
> /* We need to walk swapper, so turn off the MMU. */
> pre_disable_mmu_workaround
> - mrs x18, sctlr_el1
> - bic x18, x18, #SCTLR_ELx_M
> - msr sctlr_el1, x18
> + mrs x17, sctlr_el1
> + bic x17, x17, #SCTLR_ELx_M
> + msr sctlr_el1, x17
> isb
>
> /* Everybody is enjoying the idmap, so we can rewrite swapper. */
> @@ -281,9 +281,9 @@ skip_pgd:
> isb
>
> /* We're done: fire up the MMU again */
> - mrs x18, sctlr_el1
> - orr x18, x18, #SCTLR_ELx_M
> - msr sctlr_el1, x18
> + mrs x17, sctlr_el1
> + orr x17, x17, #SCTLR_ELx_M
> + msr sctlr_el1, x17
> isb
>
> /*
> @@ -353,46 +353,47 @@ skip_pte:
> b.ne do_pte
> b next_pmd
>
> + .unreq cpu
> + .unreq num_cpus
> + .unreq swapper_pa
> + .unreq cur_pgdp
> + .unreq end_pgdp
> + .unreq pgd
> + .unreq cur_pudp
> + .unreq end_pudp
> + .unreq pud
> + .unreq cur_pmdp
> + .unreq end_pmdp
> + .unreq pmd
> + .unreq cur_ptep
> + .unreq end_ptep
> + .unreq pte
> +
> /* Secondary CPUs end up here */
> __idmap_kpti_secondary:
> /* Uninstall swapper before surgery begins */
> - __idmap_cpu_set_reserved_ttbr1 x18, x17
> + __idmap_cpu_set_reserved_ttbr1 x16, x17
>
> /* Increment the flag to let the boot CPU we're ready */
> -1: ldxr w18, [flag_ptr]
> - add w18, w18, #1
> - stxr w17, w18, [flag_ptr]
> +1: ldxr w16, [flag_ptr]
> + add w16, w16, #1
> + stxr w17, w16, [flag_ptr]
> cbnz w17, 1b
>
> /* Wait for the boot CPU to finish messing around with swapper */
> sevl
> 1: wfe
> - ldxr w18, [flag_ptr]
> - cbnz w18, 1b
> + ldxr w16, [flag_ptr]
> + cbnz w16, 1b
>
> /* All done, act like nothing happened */
> - offset_ttbr1 swapper_ttb, x18
> + offset_ttbr1 swapper_ttb, x16
> msr ttbr1_el1, swapper_ttb
> isb
> ret
>
> - .unreq cpu
> - .unreq num_cpus
> - .unreq swapper_pa
> .unreq swapper_ttb
> .unreq flag_ptr
> - .unreq cur_pgdp
> - .unreq end_pgdp
> - .unreq pgd
> - .unreq cur_pudp
> - .unreq end_pudp
> - .unreq pud
> - .unreq cur_pmdp
> - .unreq end_pmdp
> - .unreq pmd
> - .unreq cur_ptep
> - .unreq end_ptep
> - .unreq pte
> ENDPROC(idmap_kpti_install_ng_mappings)
> .popsection
> #endif
> --
> 2.23.0.866.gb869b98d4c-goog
>
--
Thanks,
~Nick Desaulniers
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