Discussion:
[PATCH 3/3] arm64: reduce trampoline data alignment
(too old to reply)
Rémi Denis-Courmont
2020-03-16 12:40:46 UTC
Permalink
From: Rémi Denis-Courmont <***@huawei.com>

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 <***@huawei.com>
---
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
Will Deacon
2020-03-17 22:34:33 UTC
Permalink
Post by Rémi Denis-Courmont
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.
---
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 <***@kernel.org>

Will

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