The segment descriptor contains information that is relevant to how linear address need to be computed. It contains the default size of addresses as well as the base address of the segment. Thus, given a segment selector, we ought look at segment descriptor to correctly calculate the linear address.
In protected mode, the segment selector might indicate a segment descriptor from either the global descriptor table or a local descriptor table. Both cases are considered in this function. This function is the initial implementation for subsequent functions that will obtain the aforementioned attributes of the segment descriptor. Cc: Dave Hansen <[email protected]> Cc: Adam Buchbinder <[email protected]> Cc: Colin Ian King <[email protected]> Cc: Lorenzo Stoakes <[email protected]> Cc: Qiaowei Ren <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Masami Hiramatsu <[email protected]> Cc: Adrian Hunter <[email protected]> Cc: Kees Cook <[email protected]> Cc: Thomas Garnier <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Dmitry Vyukov <[email protected]> Cc: Ravi V. Shankar <[email protected]> Cc: [email protected] Signed-off-by: Ricardo Neri <[email protected]> --- arch/x86/lib/insn-eval.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 8d45df8..8608adf 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -5,9 +5,13 @@ */ #include <linux/kernel.h> #include <linux/string.h> +#include <asm/desc_defs.h> +#include <asm/desc.h> #include <asm/inat.h> #include <asm/insn.h> #include <asm/insn-eval.h> +#include <asm/ldt.h> +#include <linux/mmu_context.h> #include <asm/vm86.h> enum reg_type { @@ -294,6 +298,63 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, } /** + * get_desc() - Obtain address of segment descriptor + * @seg: Segment selector + * @desc: Pointer to the selected segment descriptor + * + * Given a segment selector, obtain a memory pointer to the segment + * descriptor. Both global and local descriptor tables are supported. + * desc will contain the address of the descriptor. + * + * Return: 0 if success, -EINVAL if failure + */ +static int get_desc(unsigned short seg, struct desc_struct **desc) +{ + struct desc_ptr gdt_desc = {0, 0}; + unsigned long desc_base; + + if (!desc) + return -EINVAL; + + desc_base = seg & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK); + +#ifdef CONFIG_MODIFY_LDT_SYSCALL + if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) { + seg >>= 3; + + mutex_lock(¤t->active_mm->context.lock); + if (unlikely(!current->active_mm->context.ldt || + seg >= current->active_mm->context.ldt->size)) { + *desc = NULL; + mutex_unlock(¤t->active_mm->context.lock); + return -EINVAL; + } + + *desc = ¤t->active_mm->context.ldt->entries[seg]; + mutex_unlock(¤t->active_mm->context.lock); + return 0; + } +#endif + native_store_gdt(&gdt_desc); + + /* + * Bits [15:3] of the segment selector contain the index. Such + * index needs to be multiplied by 8. However, as the index + * least significant bit is already in bit 3, we don't have + * to perform the multiplication. + */ + desc_base = seg & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK); + + if (desc_base > gdt_desc.size) { + *desc = NULL; + return -EINVAL; + } + + *desc = (struct desc_struct *)(gdt_desc.address + desc_base); + return 0; +} + +/** * insn_get_reg_offset_modrm_rm - Obtain register in r/m part of ModRM byte * @insn: Instruction structure containing the ModRM byte * @regs: Set of registers indicated by the ModRM byte -- 2.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
