Re: [PATCH 03/19] x86, mpx: use new tsk_get_xsave_addr()

Thomas Gleixner
2015-05-18T20:35:56Z

On Fri, 8 May 2015, Dave Hansen wrote:

> Subject: x86, mpx: use new tsk_get_xsave_addr()

-NOSUCHFUNCTION

And please let the sentence start with an upper case letter.

x86, mpx: Use ...

> #ifdef CONFIG_X86_INTEL_MPX
> siginfo_t *mpx_generate_siginfo(struct pt_regs *regs,
> - struct xsave_struct *xsave_buf);
> -int mpx_handle_bd_fault(struct xsave_struct *xsave_buf);
> + struct task_struct *tsk);
> +int mpx_handle_bd_fault(struct task_struct *tsk);

So you still keep *tsk and remove it in the next patch. I guess either
ordering has its value, so no problem to do it this way.

> 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 *
> unsigned long start, unsigned long end);
> #else
> static inline siginfo_t *mpx_generate_siginfo(struct pt_regs *regs,
> - struct xsave_struct *xsave_buf)
> + struct task_struct *tsk)

But that makes no sense. Introduce a new instance just to remove it
one patch later. So maybe cleaning up the *tsk thing first might be
the better approach, but I let you decide.

> #include <asm/mach_traps.h>
> #include <asm/alternative.h>
> #include <asm/mpx.h>
> +#include <asm/xsave.h>
>
> #ifdef CONFIG_X86_64
> #include <asm/x86_init.h>
> @@ -372,7 +373,6 @@ dotraplinkage void do_double_fault(struc
> dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
> {
> struct task_struct *tsk = current;
> - struct xsave_struct *xsave_buf;
> enum ctx_state prev_state;
> struct bndcsr *bndcsr;
> siginfo_t *info;
> @@ -393,12 +393,11 @@ dotraplinkage void do_bounds(struct pt_r
>
> /*
> * 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.
> */
> - fpu_save_init(&tsk->thread.fpu);
> - xsave_buf = &(tsk->thread.fpu.state->xsave);
> - bndcsr = get_xsave_addr(xsave_buf, XSTATE_BNDCSR);
> + bndcsr = get_xsave_field(XSTATE_BNDCSR);

Hmm, I did not notice when I looked at the patch which introduced
get_xsave_field(). But with the removed get_xsave_addr() I really had
to look twice.

get_xsave_field() suggest that you get the field content. So wouldn't
it be better to name it get_xsave_field_ptr() or such?

> if (!bndcsr)
> goto exit_trap;
>
> @@ -409,11 +408,11 @@ dotraplinkage void do_bounds(struct pt_r
> */
> 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 -puN arch/x86/mm/mpx.c~use-new-tsk_get_xsave_addr arch/x86/mm/mpx.c
> --- a/arch/x86/mm/mpx.c~use-new-tsk_get_xsave_addr 2015-05-08 11:46:11.388599581 -0700
> +++ b/arch/x86/mm/mpx.c 2015-05-08 11:46:11.393599807 -0700
> @@ -273,7 +273,7 @@ bad_opcode:
> * The caller is expected to kfree() the returned siginfo_t.
> */
> siginfo_t *mpx_generate_siginfo(struct pt_regs *regs,
> - struct xsave_struct *xsave_buf)
> + struct task_struct *tsk)

Looking at the implementation makes me wonder about the extra *tsk
argument some more ....

> {
> struct bndreg *bndregs, *bndreg;
> siginfo_t *info = NULL;
> @@ -295,8 +295,8 @@ siginfo_t *mpx_generate_siginfo(struct p
> 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 urrent task's xsave area */

urrent?

> + bndregs = get_xsave_field(XSTATE_BNDREGS);
> if (!bndregs) {
> err = -EINVAL;
> goto err_out;

Still no user of *tsk ....

> @@ -358,8 +358,7 @@ static __user void *task_get_bounds_dir(
> -int mpx_handle_bd_fault(struct xsave_struct *xsave_buf)
> +int mpx_handle_bd_fault(struct task_struct *tsk)
> {
> /*
> * Userspace never asked us to manage the bounds tables,
> @@ -535,7 +534,7 @@ int mpx_handle_bd_fault(struct xsave_str
> if (!kernel_managing_mpx_tables(current->mm))
> return -EINVAL;
>
> - if (do_mpx_bt_fault(xsave_buf)) {
> + if (do_mpx_bt_fault(tsk)) {

Same problem actually with do_mpx_bt_fault().

Thanks,

tglx