From a84eeaa96b36a03188e1423349669c108d3a4bd7 Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Sun, 7 Jun 2015 11:37:01 -0700 Subject: [PATCH] x86/mpx: Use the new get_xsave_field_ptr()API The MPX registers (bndcsr/bndcfgu/bndstatus) are not directly accessible via normal instructions. They essentially act as if they were floating point registers and are saved/restored along with those registers. There are two main paths in the MPX code where we care about the contents of these registers: 1. #BR (bounds) faults 2. the prctl() code where we are setting MPX up Both of those paths _might_ be called without the FPU having been used. That means that 'tsk->thread.fpu.state' might never be allocated. Also, fpu_save_init() is not preempt-safe. It was a bug to call it without disabling preemption. The new get_xsave_addr() calls unlazy_fpu() instead and properly disables preemption. Signed-off-by: Dave Hansen Reviewed-by: Thomas Gleixner Cc: Andrew Morton Cc: Andy Lutomirski Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Rik van Riel Cc: Suresh Siddha Cc: bp@alien8.de Link: http://lkml.kernel.org/r/20150607183701.BC0D37CF@viggo.jf.intel.com Signed-off-by: Ingo Molnar --- arch/x86/include/asm/mpx.h | 8 ++++---- arch/x86/kernel/traps.c | 17 ++++++++--------- arch/x86/mm/mpx.c | 30 +++++++++++++++--------------- 3 files changed, 27 insertions(+), 28 deletions(-) diff --git a/arch/x86/include/asm/mpx.h b/arch/x86/include/asm/mpx.h index f3c1b71d4fae..39f2d0ffe1e2 100644 --- a/arch/x86/include/asm/mpx.h +++ b/arch/x86/include/asm/mpx.h @@ -60,8 +60,8 @@ #ifdef CONFIG_X86_INTEL_MPX siginfo_t *mpx_generate_siginfo(struct pt_regs *regs, - struct xregs_state *xsave_buf); -int mpx_handle_bd_fault(struct xregs_state *xsave_buf); + struct task_struct *tsk); +int mpx_handle_bd_fault(struct task_struct *tsk); static inline int kernel_managing_mpx_tables(struct mm_struct *mm) { return (mm->bd_addr != MPX_INVALID_BOUNDS_DIR); @@ -78,11 +78,11 @@ void mpx_notify_unmap(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long start, unsigned long end); #else static inline siginfo_t *mpx_generate_siginfo(struct pt_regs *regs, - struct xregs_state *xsave_buf) + struct task_struct *tsk) { return NULL; } -static inline int mpx_handle_bd_fault(struct xregs_state *xsave_buf) +static inline int mpx_handle_bd_fault(struct task_struct *tsk) { return -EINVAL; } diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index a2510f230195..42f15314b361 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -59,6 +59,7 @@ #include #include #include +#include #include #ifdef CONFIG_X86_64 @@ -371,9 +372,8 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code) dotraplinkage void do_bounds(struct pt_regs *regs, long error_code) { struct task_struct *tsk = current; - struct xregs_state *xsave_buf; enum ctx_state prev_state; - struct bndcsr *bndcsr; + const struct bndcsr *bndcsr; siginfo_t *info; prev_state = exception_enter(); @@ -392,12 +392,11 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code) /* * We need to look at BNDSTATUS to resolve this exception. - * It is not directly accessible, though, so we need to - * do an xsave and then pull it out of the xsave buffer. + * A NULL here might mean that it is in its 'init state', + * which is all zeros which indicates MPX was not + * responsible for the exception. */ - copy_fpregs_to_fpstate(&tsk->thread.fpu); - xsave_buf = &(tsk->thread.fpu.state.xsave); - bndcsr = get_xsave_addr(xsave_buf, XSTATE_BNDCSR); + bndcsr = get_xsave_field_ptr(XSTATE_BNDCSR); if (!bndcsr) goto exit_trap; @@ -408,11 +407,11 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code) */ switch (bndcsr->bndstatus & MPX_BNDSTA_ERROR_CODE) { case 2: /* Bound directory has invalid entry. */ - if (mpx_handle_bd_fault(xsave_buf)) + if (mpx_handle_bd_fault(tsk)) goto exit_trap; break; /* Success, it was handled */ case 1: /* Bound violation. */ - info = mpx_generate_siginfo(regs, xsave_buf); + info = mpx_generate_siginfo(regs, tsk); if (IS_ERR(info)) { /* * We failed to decode the MPX instruction. Act as if diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 2e0dfd39bd22..9d67e230b4fb 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -272,9 +272,9 @@ bad_opcode: * The caller is expected to kfree() the returned siginfo_t. */ siginfo_t *mpx_generate_siginfo(struct pt_regs *regs, - struct xregs_state *xsave_buf) + struct task_struct *tsk) { - struct bndreg *bndregs, *bndreg; + const struct bndreg *bndregs, *bndreg; siginfo_t *info = NULL; struct insn insn; uint8_t bndregno; @@ -294,8 +294,8 @@ siginfo_t *mpx_generate_siginfo(struct pt_regs *regs, err = -EINVAL; goto err_out; } - /* get the bndregs _area_ of the xsave structure */ - bndregs = get_xsave_addr(xsave_buf, XSTATE_BNDREGS); + /* get bndregs field from current task's xsave area */ + bndregs = get_xsave_field_ptr(XSTATE_BNDREGS); if (!bndregs) { err = -EINVAL; goto err_out; @@ -342,7 +342,7 @@ err_out: static __user void *task_get_bounds_dir(struct task_struct *tsk) { - struct bndcsr *bndcsr; + const struct bndcsr *bndcsr; if (!cpu_feature_enabled(X86_FEATURE_MPX)) return MPX_INVALID_BOUNDS_DIR; @@ -357,8 +357,7 @@ static __user void *task_get_bounds_dir(struct task_struct *tsk) * The bounds directory pointer is stored in a register * only accessible if we first do an xsave. */ - copy_fpregs_to_fpstate(&tsk->thread.fpu); - bndcsr = get_xsave_addr(&tsk->thread.fpu.state.xsave, XSTATE_BNDCSR); + bndcsr = get_xsave_field_ptr(XSTATE_BNDCSR); if (!bndcsr) return MPX_INVALID_BOUNDS_DIR; @@ -389,9 +388,10 @@ int mpx_enable_management(struct task_struct *tsk) * directory into XSAVE/XRSTOR Save Area and enable MPX through * XRSTOR instruction. * - * copy_xregs_to_kernel() is expected to be very expensive. Storing the bounds - * directory here means that we do not have to do xsave in the unmap - * path; we can just use mm->bd_addr instead. + * The copy_xregs_to_kernel() beneath get_xsave_field_ptr() is + * expected to be relatively expensive. Storing the bounds + * directory here means that we do not have to do xsave in the + * unmap path; we can just use mm->bd_addr instead. */ bd_base = task_get_bounds_dir(tsk); down_write(&mm->mmap_sem); @@ -497,12 +497,12 @@ out_unmap: * bound table is 16KB. With 64-bit mode, the size of BD is 2GB, * and the size of each bound table is 4MB. */ -static int do_mpx_bt_fault(struct xregs_state *xsave_buf) +static int do_mpx_bt_fault(struct task_struct *tsk) { unsigned long bd_entry, bd_base; - struct bndcsr *bndcsr; + const struct bndcsr *bndcsr; - bndcsr = get_xsave_addr(xsave_buf, XSTATE_BNDCSR); + bndcsr = get_xsave_field_ptr(XSTATE_BNDCSR); if (!bndcsr) return -EINVAL; /* @@ -525,7 +525,7 @@ static int do_mpx_bt_fault(struct xregs_state *xsave_buf) return allocate_bt((long __user *)bd_entry); } -int mpx_handle_bd_fault(struct xregs_state *xsave_buf) +int mpx_handle_bd_fault(struct task_struct *tsk) { /* * Userspace never asked us to manage the bounds tables, @@ -534,7 +534,7 @@ int mpx_handle_bd_fault(struct xregs_state *xsave_buf) if (!kernel_managing_mpx_tables(current->mm)) return -EINVAL; - if (do_mpx_bt_fault(xsave_buf)) { + if (do_mpx_bt_fault(tsk)) { force_sig(SIGSEGV, current); /* * The force_sig() is essentially "handling" this -- 2.20.1