Re: [PATCH 5.4 18/43] arm64: entry: Add macro for reading symbol addresses from the trampoline

Florian Fainelli
2022-03-18T16:33:36Z

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