2020-03-16 12:41:17

by Rémi Denis-Courmont

Subject: [PATCH 3/3] arm64: reduce trampoline data alignment

From: Rémi Denis-Courmont <[email protected]>

The trampoline data, currently consisting of two relocated pointers,
must be within a single page. However, there are no needs for it to
start a page.

This reduces the alignment to 16 bytes (with SDEI) or 8 bytes (without
SDEI), which is sufficient to ensure that the data is entirely within a
single page of the fixmap.

Signed-off-by: Rémi Denis-Courmont <[email protected]>
---
arch/arm64/kernel/entry.S | 4 ++--
arch/arm64/mm/mmu.c | 5 ++---
2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index af17fcb4aaea..b648f9fe1e33 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -858,12 +858,12 @@ SYM_CODE_END(tramp_exit_compat)
.popsection // .entry.tramp.text
#ifdef CONFIG_RANDOMIZE_BASE
.pushsection ".rodata", "a"
- .align PAGE_SHIFT
#ifdef CONFIG_ARM_SDE_INTERFACE
+ .align 4 // all .rodata must be in a single fixmap page
SYM_DATA_START(__sdei_asm_trampoline_next_handler)
.quad __sdei_asm_handler
SYM_DATA_END(__sdei_asm_trampoline_next_handler)
-#endif
+#endif /* CONFIG_ARM_SDE_INTERFACE */
SYM_DATA_START(__entry_tramp_data_start)
.quad vectors
SYM_DATA_END(__entry_tramp_data_start)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 9b08f7c7e6f0..6a0e75f48e7b 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -599,9 +599,8 @@ static int __init map_entry_trampoline(void)
if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
extern char __entry_tramp_data_start[];

- __set_fixmap(FIX_ENTRY_TRAMP_DATA,
- __pa_symbol(__entry_tramp_data_start),
- PAGE_KERNEL_RO);
+ pa_start = __pa_symbol(__entry_tramp_data_start) & PAGE_MASK;
+ __set_fixmap(FIX_ENTRY_TRAMP_DATA, pa_start, PAGE_KERNEL_RO);
}

return 0;
--
2.25.1

2020-03-17 22:37:00

by Will Deacon

Subject: Re: [PATCH 3/3] arm64: reduce trampoline data alignment

On Mon, Mar 16, 2020 at 02:40:46PM +0200, R?mi Denis-Courmont wrote:
> From: R?mi Denis-Courmont <[email protected]>
>
> The trampoline data, currently consisting of two relocated pointers,
> must be within a single page. However, there are no needs for it to
> start a page.
>
> This reduces the alignment to 16 bytes (with SDEI) or 8 bytes (without
> SDEI), which is sufficient to ensure that the data is entirely within a
> single page of the fixmap.
>
> Signed-off-by: R?mi Denis-Courmont <[email protected]>
> ---
> arch/arm64/kernel/entry.S | 4 ++--
> arch/arm64/mm/mmu.c | 5 ++---
> 2 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index af17fcb4aaea..b648f9fe1e33 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -858,12 +858,12 @@ SYM_CODE_END(tramp_exit_compat)
> .popsection // .entry.tramp.text
> #ifdef CONFIG_RANDOMIZE_BASE
> .pushsection ".rodata", "a"
> - .align PAGE_SHIFT
> #ifdef CONFIG_ARM_SDE_INTERFACE
> + .align 4 // all .rodata must be in a single fixmap page
> SYM_DATA_START(__sdei_asm_trampoline_next_handler)
> .quad __sdei_asm_handler
> SYM_DATA_END(__sdei_asm_trampoline_next_handler)
> -#endif
> +#endif /* CONFIG_ARM_SDE_INTERFACE */
> SYM_DATA_START(__entry_tramp_data_start)
> .quad vectors
> SYM_DATA_END(__entry_tramp_data_start)
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 9b08f7c7e6f0..6a0e75f48e7b 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -599,9 +599,8 @@ static int __init map_entry_trampoline(void)
> if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> extern char __entry_tramp_data_start[];
>
> - __set_fixmap(FIX_ENTRY_TRAMP_DATA,
> - __pa_symbol(__entry_tramp_data_start),
> - PAGE_KERNEL_RO);
> + pa_start = __pa_symbol(__entry_tramp_data_start) & PAGE_MASK;
> + __set_fixmap(FIX_ENTRY_TRAMP_DATA, pa_start, PAGE_KERNEL_RO);
> }
>
> return 0;

Acked-by: Will Deacon <[email protected]>

Will