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    SubjectRe: [PATCH 5.4 18/43] arm64: entry: Add macro for reading symbol addresses from the trampoline
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    On 3/18/2022 5:11 AM, James Morse wrote:
    > Hi Florian,
    >
    > On 3/17/22 8:48 PM, Florian Fainelli wrote:
    >> On 3/17/22 5:45 AM, Greg Kroah-Hartman wrote:
    >>> From: James Morse <james.morse@arm.com>
    >>>
    >>> commit b28a8eebe81c186fdb1a0078263b30576c8e1f42 upstream.
    >>>
    >>> The trampoline code needs to use the address of symbols in the wider
    >>> kernel, e.g. vectors. PC-relative addressing wouldn't work as the
    >>> trampoline code doesn't run at the address the linker expected.
    >>>
    >>> tramp_ventry uses a literal pool, unless CONFIG_RANDOMIZE_BASE is
    >>> set, in which case it uses the data page as a literal pool because
    >>> the data page can be unmapped when running in user-space, which is
    >>> required for CPUs vulnerable to meltdown.
    >>>
    >>> Pull this logic out as a macro, instead of adding a third copy
    >>> of it.
    >>>
    >>> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
    >>> Signed-off-by: James Morse <james.morse@arm.com>
    >>> Signed-off-by: Sasha Levin <sashal@kernel.org>
    >>
    >> This commit causes a linking failure with CONFIG_ARM_SDE_INTERFACE=y
    >> enabled in the kernel:
    >>
    >>    LD      .tmp_vmlinux.kallsyms1
    >> /local/users/fainelli/buildroot/output/arm64/host/bin/aarch64-linux-ld:
    >> arch/arm64/kernel/entry.o: in function `__sdei_asm_exit_trampoline':
    >> /local/users/fainelli/buildroot/output/arm64/build/linux-custom/arch/arm64/kernel/entry.S:1352:
    >>
    >> undefined reference to `__sdei_asm_trampoline_next_handler'
    >> make[2]: *** [Makefile:1100: vmlinux] Error 1
    >> make[1]: *** [package/pkg-generic.mk:295:
    >> /local/users/fainelli/buildroot/output/arm64/build/linux-custom/.stamp_built]
    >>
    >> Error 2
    >> make: *** [Makefile:27: _all] Error 2
    >
    > ... and with CONFIG_RANDOMIZE_BASE turned off, which is why allyesconfig
    > didn't catch it.

    Yes that is correct CONFIG_RANDOMIZE_BASE is turned off in the
    configuration file I used.

    > This is because I kept the next_handler bit of the label when it
    > conflicted, which isn't needed
    > because the __entry_tramp bit added by the macro serves the same purpose.
    >
    > The below diff fixes it:
    > ----------%<----------
    > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
    > index e4b5a15c2e2e..cfc0bb6c49f7 100644
    > --- a/arch/arm64/kernel/entry.S
    > +++ b/arch/arm64/kernel/entry.S
    > @@ -1190,7 +1190,7 @@ __entry_tramp_data_start:
    >  __entry_tramp_data_vectors:
    >         .quad   vectors
    >  #ifdef CONFIG_ARM_SDE_INTERFACE
    > -__entry_tramp_data___sdei_asm_trampoline_next_handler:
    > +__entry_tramp_data___sdei_asm_handler:
    >         .quad   __sdei_asm_handler
    >  #endif /* CONFIG_ARM_SDE_INTERFACE */
    >         .popsection                             // .rodata
    > @@ -1319,7 +1319,7 @@ ENTRY(__sdei_asm_entry_trampoline)
    >          */
    >  1:     str     x4, [x1, #(SDEI_EVENT_INTREGS + S_ORIG_ADDR_LIMIT)]
    >
    > -       tramp_data_read_var     x4, __sdei_asm_trampoline_next_handler
    > +       tramp_data_read_var     x4, __sdei_asm_handler
    >         br      x4
    >  ENDPROC(__sdei_asm_entry_trampoline)
    >  NOKPROBE(__sdei_asm_entry_trampoline)
    > ----------%<----------
    >
    > Good news - this didn't happen with v5.10.
    >
    > I don't see this in v5.4.185 yet.
    >
    > Greg/Sasha, what is least work for you?:
    > A new version of this patch,
    > A fixup on top of the series,
    > Reposting the series with this fixed.

    FWIW, applying your patch on top of the entire 5.4.186-rc1 series will
    fail with some rejects so that would require you to fixup the patch
    instead, and then I suppose the whole -rc1 now becomes an -rc2?

    >
    >
    > Thanks for catching this!

    Thanks for the quick turnaround:

    Tested-by: Florian Fainelli <f.fainelli@gmail.com>
    --
    Florian

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