On Tue, 2017-09-26 at 20:05 +0200, Borislav Petkov wrote: > On Fri, Aug 18, 2017 at 05:27:54PM -0700, Ricardo Neri wrote: > > > > The segment descriptor contains information that is relevant to how > > linear > > addresses 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 > ^ > to
I will correct this syntax error. > > > > > 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 a prerequisite for functions in subsequent commits > > 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 | 55 > > ++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 55 insertions(+) > > > > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c > > index 86f58ce6c302..9cf2c49afc15 100644 > > --- a/arch/x86/lib/insn-eval.c > > +++ b/arch/x86/lib/insn-eval.c > > @@ -6,9 +6,13 @@ > > #include <linux/kernel.h> > > #include <linux/string.h> > > #include <linux/ratelimit.h> > > +#include <linux/mmu_context.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 <asm/vm86.h> > > > > enum reg_type { > > @@ -402,6 +406,57 @@ static int get_reg_offset(struct insn *insn, > > struct pt_regs *regs, > > } > > > > /** > > + * get_desc() - Obtain address of segment descriptor > Get segment descriptor. > > > > > + * @sel: Segment selector > > + * > > + * Given a segment selector, obtain a pointer to the segment > > descriptor. > > + * Both global and local descriptor tables are supported. > > + * > > + * Return: pointer to segment descriptor on success. NULL on > > error. > > + */ > > +static struct desc_struct *get_desc(unsigned short sel) > I've simplified this function to be more readable, here's a diff > ontop. > > More specifically, if you flip the logic and move @desc inside the > if, > you don't need to have mutex_unlock() twice in there. > > And having a local @ldt ptr makes the selector check more readable. > > --- > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c > index 9cf2c49afc15..48af787cb160 100644 > --- a/arch/x86/lib/insn-eval.c > +++ b/arch/x86/lib/insn-eval.c > @@ -417,24 +417,24 @@ static int get_reg_offset(struct insn *insn, > struct pt_regs *regs, > static struct desc_struct *get_desc(unsigned short sel) > { > struct desc_ptr gdt_desc = {0, 0}; > - struct desc_struct *desc = NULL; > unsigned long desc_base; > > #ifdef CONFIG_MODIFY_LDT_SYSCALL > if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT) { > + struct desc_struct *desc = NULL; > + struct ldt_struct *ldt; > + > /* Bits [15:3] contain the index of the desired > entry. */ > sel >>= 3; > > mutex_lock(¤t->active_mm->context.lock); > - /* The size of the LDT refers to the number of > entries. */ > - if (!current->active_mm->context.ldt || > - sel >= current->active_mm->context.ldt- > >nr_entries) { > - mutex_unlock(¤t->active_mm- > >context.lock); > - return NULL; > - } > > - desc = ¤t->active_mm->context.ldt- > >entries[sel]; > + ldt = current->active_mm->context.ldt; > + if (ldt && sel < ldt->nr_entries) > + desc = &ldt->entries[sel]; > + > mutex_unlock(¤t->active_mm->context.lock); > + > return desc; > } > #endif > @@ -452,8 +452,7 @@ static struct desc_struct *get_desc(unsigned > short sel) > if (desc_base > gdt_desc.size) > return NULL; > > - desc = (struct desc_struct *)(gdt_desc.address + desc_base); > - return desc; > + return (struct desc_struct *)(gdt_desc.address + desc_base); I have incorporated these changes in my code. Thanks and BR, Ricardo
