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

[Greg Kroah-Hartman]

On Fri, Mar 18, 2022 at 12:11:32PM +0000, 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@xxxxxxx>
> > > 
> > > 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@xxxxxxx>
> > > Signed-off-by: James Morse <james.morse@xxxxxxx>
> > > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > 
> > 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.
> 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.

Let me merge this into this commit.

thanks!

greg k-h