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SubjectRe: [PATCH v5] x86: make sure IDT is page aligned
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On Tue, 2013-07-16 at 11:34 -0700, Kees Cook wrote:
> Since the IDT is referenced from a fixmap, make sure it is page aligned.
> Merge with 32-bit one, since it was already aligned to deal with F00F
> bug. Since bss is cleared before IDT setup, it can live there. This also
> moves the other *_idt_table variables into common locations.
>
> This avoids the risk of the IDT ever being moved in the bss and having
> the mapping be offset, resulting in calling incorrect handlers. In the
> current upstream kernel this is not a manifested bug, but heavily patched
> kernels (such as those using the PaX patch series) did encounter this bug.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Reported-by: PaX Team <pageexec@gmail.com>


I like it just because it removes those nasty #ifdef blocks for x86_64
or not.

Acked-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve

> ---
> v5:
> - add comments to all IDTs about alignment reasoning, suggested by Linus
> v4:
> - rework using __page_aligned_bss, suggested by Yinghai LU
> - move all the other IDT variables as well, suggested by HPA
> v3:
> - merge 32-bit and 64-bit idt_table definition
> v2:
> - 32-bit was already aligned
> ---
> arch/x86/kernel/head_64.S | 15 ---------------
> arch/x86/kernel/tracepoint.c | 6 ++----
> arch/x86/kernel/traps.c | 12 ++++++------
> 3 files changed, 8 insertions(+), 25 deletions(-)
>
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index 5e4d8a8..e1aabdb 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -512,21 +512,6 @@ ENTRY(phys_base)
>
> #include "../../x86/xen/xen-head.S"
>
> - .section .bss, "aw", @nobits
> - .align L1_CACHE_BYTES
> -ENTRY(idt_table)
> - .skip IDT_ENTRIES * 16
> -
> - .align L1_CACHE_BYTES
> -ENTRY(debug_idt_table)
> - .skip IDT_ENTRIES * 16
> -
> -#ifdef CONFIG_TRACING
> - .align L1_CACHE_BYTES
> -ENTRY(trace_idt_table)
> - .skip IDT_ENTRIES * 16
> -#endif
> -
> __PAGE_ALIGNED_BSS
> NEXT_PAGE(empty_zero_page)
> .skip PAGE_SIZE
> diff --git a/arch/x86/kernel/tracepoint.c b/arch/x86/kernel/tracepoint.c
> index 4e584a8..1c113db 100644
> --- a/arch/x86/kernel/tracepoint.c
> +++ b/arch/x86/kernel/tracepoint.c
> @@ -12,10 +12,8 @@ atomic_t trace_idt_ctr = ATOMIC_INIT(0);
> struct desc_ptr trace_idt_descr = { NR_VECTORS * 16 - 1,
> (unsigned long) trace_idt_table };
>
> -#ifndef CONFIG_X86_64
> -gate_desc trace_idt_table[NR_VECTORS] __page_aligned_data
> - = { { { { 0, 0 } } }, };
> -#endif
> +/* No need to be aligned, but done to keep all IDTs defined the same way. */
> +gate_desc trace_idt_table[NR_VECTORS] __page_aligned_bss;
>
> static int trace_irq_vector_refcount;
> static DEFINE_MUTEX(irq_vector_mutex);
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index b0865e8..1b23a1c 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -63,19 +63,19 @@
> #include <asm/x86_init.h>
> #include <asm/pgalloc.h>
> #include <asm/proto.h>
> +
> +/* No need to be aligned, but done to keep all IDTs defined the same way. */
> +gate_desc debug_idt_table[NR_VECTORS] __page_aligned_bss;
> #else
> #include <asm/processor-flags.h>
> #include <asm/setup.h>
>
> asmlinkage int system_call(void);
> -
> -/*
> - * The IDT has to be page-aligned to simplify the Pentium
> - * F0 0F bug workaround.
> - */
> -gate_desc idt_table[NR_VECTORS] __page_aligned_data = { { { { 0, 0 } } }, };
> #endif
>
> +/* Must be page-aligned because the real IDT is used in a fixmap. */
> +gate_desc idt_table[NR_VECTORS] __page_aligned_bss;
> +
> DECLARE_BITMAP(used_vectors, NR_VECTORS);
> EXPORT_SYMBOL_GPL(used_vectors);
>
> --
> 1.7.9.5
>
>




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