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SubjectRe: [Patch V2] x86/ldt: correct fpu emulation access to ldt
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Please ignore, V3 coming soon.


Juergen

On 08/06/2015 11:07 AM, Juergen Gross wrote:
> Commit 37868fe113ff ("x86/ldt: Make modify_ldt synchronous") introduced
> a new struct ldt_struct anchored at mm->context.ldt.
>
> Adapt the x86 fpu emulation to use that new structure.
>
> Cc: <stable@vger.kernel.org> # 37868fe113ff: x86/ldt: Make modify_ldt synchronous
> Cc: <stable@vger.kernel.org> # a5b9e5a2f14f: x86/ldt: Make modify_ldt optional
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
> arch/x86/math-emu/fpu_entry.c | 3 +--
> arch/x86/math-emu/fpu_system.h | 18 +++++++++++++++---
> arch/x86/math-emu/get_address.c | 3 +--
> 3 files changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/math-emu/fpu_entry.c b/arch/x86/math-emu/fpu_entry.c
> index f37e84a..203318a 100644
> --- a/arch/x86/math-emu/fpu_entry.c
> +++ b/arch/x86/math-emu/fpu_entry.c
> @@ -29,7 +29,6 @@
>
> #include <asm/uaccess.h>
> #include <asm/traps.h>
> -#include <asm/desc.h>
> #include <asm/user.h>
> #include <asm/fpu/internal.h>
>
> @@ -181,7 +180,7 @@ void math_emulate(struct math_emu_info *info)
> math_abort(FPU_info, SIGILL);
> }
>
> - code_descriptor = LDT_DESCRIPTOR(FPU_CS);
> + code_descriptor = *FPU_get_ldt_descriptor(FPU_CS);
> if (SEG_D_SIZE(code_descriptor)) {
> /* The above test may be wrong, the book is not clear */
> /* Segmented 32 bit protected mode */
> diff --git a/arch/x86/math-emu/fpu_system.h b/arch/x86/math-emu/fpu_system.h
> index 9ccecb6..9330583 100644
> --- a/arch/x86/math-emu/fpu_system.h
> +++ b/arch/x86/math-emu/fpu_system.h
> @@ -16,9 +16,21 @@
> #include <linux/kernel.h>
> #include <linux/mm.h>
>
> -/* s is always from a cpu register, and the cpu does bounds checking
> - * during register load --> no further bounds checks needed */
> -#define LDT_DESCRIPTOR(s) (((struct desc_struct *)current->mm->context.ldt)[(s) >> 3])
> +#include <asm/desc.h>
> +#include <asm/mmu_context.h>
> +
> +static inline struct desc_struct *FPU_get_ldt_descriptor(unsigned seg)
> +{
> + static struct desc_struct zero_desc;
> +
> +#ifdef CONFIG_MODIFY_LDT_SYSCALL
> + seg >>= 3;
> + if (seg < current->mm->context.ldt->size)
> + return current->mm->context.ldt->entries + seg;
> +#endif
> + return &zero_desc;
> +}
> +
> #define SEG_D_SIZE(x) ((x).b & (3 << 21))
> #define SEG_G_BIT(x) ((x).b & (1 << 23))
> #define SEG_GRANULARITY(x) (((x).b & (1 << 23)) ? 4096 : 1)
> diff --git a/arch/x86/math-emu/get_address.c b/arch/x86/math-emu/get_address.c
> index 6ef5e99..f912edd 100644
> --- a/arch/x86/math-emu/get_address.c
> +++ b/arch/x86/math-emu/get_address.c
> @@ -20,7 +20,6 @@
> #include <linux/stddef.h>
>
> #include <asm/uaccess.h>
> -#include <asm/desc.h>
>
> #include "fpu_system.h"
> #include "exception.h"
> @@ -158,7 +157,7 @@ static long pm_address(u_char FPU_modrm, u_char segment,
> addr->selector = PM_REG_(segment);
> }
>
> - descriptor = LDT_DESCRIPTOR(PM_REG_(segment));
> + descriptor = *FPU_get_ldt_descriptor(segment);
> base_address = SEG_BASE_ADDR(descriptor);
> address = base_address + offset;
> limit = base_address
>



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