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

Florian Fainelli
2022-03-17T20:48:11Z

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