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Subject: Re: [PATCH 5.4 18/43] arm64: entry: Add macro for reading symbol
 addresses from the trampoline
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Cc:     stable@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
        James Morse <james.morse@arm.com>,
        Sasha Levin <sashal@kernel.org>
References: <20220317124527.672236844@linuxfoundation.org>
 <20220317124528.180267687@linuxfoundation.org>
From:   Florian Fainelli <f.fainelli@gmail.com>
Message-ID: <113e7675-4263-2a20-81d0-9634f03511d2@gmail.com>
Date:   Thu, 17 Mar 2022 13:48:02 -0700
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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


> ---
>  arch/arm64/kernel/entry.S | 35 ++++++++++++++++-------------------
>  1 file changed, 16 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 14351ee5e812..e4b5a15c2e2e 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -1063,6 +1063,15 @@ alternative_else_nop_endif
>  	sub	\dst, \dst, PAGE_SIZE
>  	.endm
>  
> +	.macro tramp_data_read_var	dst, var
> +#ifdef CONFIG_RANDOMIZE_BASE
> +	tramp_data_page		\dst
> +	add	\dst, \dst, #:lo12:__entry_tramp_data_\var
> +	ldr	\dst, [\dst]
> +#else
> +	ldr	\dst, =\var
> +#endif
> +	.endm
>  
>  #define BHB_MITIGATION_NONE	0
>  #define BHB_MITIGATION_LOOP	1
> @@ -1093,13 +1102,8 @@ alternative_else_nop_endif
>  	b	.
>  2:
>  	tramp_map_kernel	x30
> -#ifdef CONFIG_RANDOMIZE_BASE
> -	tramp_data_page		x30
>  alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003
> -	ldr	x30, [x30]
> -#else
> -	ldr	x30, =vectors
> -#endif
> +	tramp_data_read_var	x30, vectors
>  alternative_if_not ARM64_WORKAROUND_CAVIUM_TX2_219_PRFM
>  	prfm	plil1strm, [x30, #(1b - \vector_start)]
>  alternative_else_nop_endif
> @@ -1183,7 +1187,12 @@ END(tramp_exit_compat)
>  	.align PAGE_SHIFT
>  	.globl	__entry_tramp_data_start
>  __entry_tramp_data_start:
> +__entry_tramp_data_vectors:
>  	.quad	vectors
> +#ifdef CONFIG_ARM_SDE_INTERFACE
> +__entry_tramp_data___sdei_asm_trampoline_next_handler:
> +	.quad	__sdei_asm_handler
> +#endif /* CONFIG_ARM_SDE_INTERFACE */
>  	.popsection				// .rodata
>  #endif /* CONFIG_RANDOMIZE_BASE */
>  #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
> @@ -1310,13 +1319,7 @@ ENTRY(__sdei_asm_entry_trampoline)
>  	 */
>  1:	str	x4, [x1, #(SDEI_EVENT_INTREGS + S_ORIG_ADDR_LIMIT)]
>  
> -#ifdef CONFIG_RANDOMIZE_BASE
> -	tramp_data_page		x4
> -	add	x4, x4, #:lo12:__sdei_asm_trampoline_next_handler
> -	ldr	x4, [x4]
> -#else
> -	ldr	x4, =__sdei_asm_handler
> -#endif
> +	tramp_data_read_var     x4, __sdei_asm_trampoline_next_handler
>  	br	x4
>  ENDPROC(__sdei_asm_entry_trampoline)
>  NOKPROBE(__sdei_asm_entry_trampoline)
> @@ -1339,12 +1342,6 @@ ENDPROC(__sdei_asm_exit_trampoline)
>  NOKPROBE(__sdei_asm_exit_trampoline)
>  	.ltorg
>  .popsection		// .entry.tramp.text
> -#ifdef CONFIG_RANDOMIZE_BASE
> -.pushsection ".rodata", "a"
> -__sdei_asm_trampoline_next_handler:
> -	.quad	__sdei_asm_handler
> -.popsection		// .rodata
> -#endif /* CONFIG_RANDOMIZE_BASE */
>  #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
>  
>  /*
> 


-- 
Florian