Messages in this thread Patch in this message |  | | From | Joerg Roedel <> | Subject | [PATCH] x86/idt: Make sure idt_table takes a whole page | Date | Thu, 9 Jul 2020 12:33:55 +0200 |
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From: Joerg Roedel <jroedel@suse.de>
On x86-32 the idt_table with 256 entries needs only 2048 bytes. It is page-aligned, but the end of the .bss..page_aligned section is not guaranteed to be page-aligned.
As a result, symbols from other .bss sections may end up on the same 4k page as the idt_table, and will accidentially get mapped read-only during boot, causing unexpected page-faults when the kernel writes to them.
Avoid this by making the idt_table 4kb in size even on x86-32. On x86-64 the idt_table is already 4kb large, so nothing changes there.
Fixes: 3e77abda65b1c ("x86/idt: Consolidate idt functionality") Signed-off-by: Joerg Roedel <jroedel@suse.de> --- arch/x86/kernel/idt.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c index 0db21206f2f3..83e24f837127 100644 --- a/arch/x86/kernel/idt.c +++ b/arch/x86/kernel/idt.c @@ -157,8 +157,13 @@ static const __initconst struct idt_data apic_idts[] = { #endif }; -/* Must be page-aligned because the real IDT is used in the cpu entry area */ -static gate_desc idt_table[IDT_ENTRIES] __page_aligned_bss; +/* + * Must be page-aligned because the real IDT is used in the cpu entry area. + * Allocate more entries than needed so that idt_table takes a whole page, so it + * is safe to map the idt_table read-only and into the user-space page-table. + */ +#define IDT_ENTRIES_ALLOCATED (PAGE_SIZE / sizeof(gate_desc)) +static gate_desc idt_table[IDT_ENTRIES_ALLOCATED] __page_aligned_bss; struct desc_ptr idt_descr __ro_after_init = { .size = IDT_TABLE_SIZE - 1, @@ -335,6 +340,9 @@ void __init idt_setup_apic_and_irq_gates(void) idt_map_in_cea(); load_idt(&idt_descr); + BUILD_BUG_ON(IDT_ENTRIES_ALLOCATED < IDT_ENTRIES); + BUILD_BUG_ON(sizeof(idt_table) != PAGE_SIZE); + /* Make the IDT table read only */ set_memory_ro((unsigned long)&idt_table, 1); -- 2.27.0
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