Re: [PATCH v4 13/16] ARM: Add an emulate flag to the kprobes/uprobesinstruction decode functions

[David Long]

On 12/20/13 09:58, Jon Medhurst (Tixy) wrote:
> On Sun, 2013-12-15 at 23:08 -0500, David Long wrote:
> > From: "David A. Long" <dave.long@xxxxxxxxxx>
> >
> > Add an emulate flag into the instruction interpreter, primarily for uprobes
> > support.
> >
> > Signed-off-by: David A. Long <dave.long@xxxxxxxxxx>
> > ---
> >   arch/arm/kernel/kprobes.c      |  3 ++-
> >   arch/arm/kernel/kprobes.h      |  1 +
> >   arch/arm/kernel/probes-arm.c   |  4 ++--
> >   arch/arm/kernel/probes-arm.h   |  2 +-
> >   arch/arm/kernel/probes-thumb.c |  8 ++++----
> >   arch/arm/kernel/probes-thumb.h |  4 ++--
> >   arch/arm/kernel/probes.c       | 32 +++++++++++++++++++++++---------
> >   arch/arm/kernel/probes.h       |  2 +-
> >   8 files changed, 36 insertions(+), 20 deletions(-)
> >
> > diff --git a/arch/arm/kernel/kprobes.c b/arch/arm/kernel/kprobes.c
> > index 0d9d49b..04690f9 100644
> > --- a/arch/arm/kernel/kprobes.c
> > +++ b/arch/arm/kernel/kprobes.c
> > @@ -87,7 +87,8 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
> >   	p->opcode = insn;
> >   	p->ainsn.insn = tmp_insn;
> >
> > -	switch ((*decode_insn)(insn, &p->ainsn, actions)) {
> > +	switch ((*decode_insn)(insn, &p->ainsn,
> > +			       true, actions)) {
>
> Any reason why the function args need splitting over two lines?

I undid the that change.

> >   	case INSN_REJECTED:	/* not supported */
> >   		return -EINVAL;
>
> [...]
>
> > --- a/arch/arm/kernel/probes.c
> > +++ b/arch/arm/kernel/probes.c
> > @@ -193,7 +193,7 @@ void __kprobes probes_emulate_none(probes_opcode_t opcode,
> >    */
> >   static probes_opcode_t __kprobes
> >   prepare_emulated_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
> > -								bool thumb)
> > +			bool thumb)
>
> Seems like a spurious indentation change.

Fixed.

> >   {
> >   #ifdef CONFIG_THUMB2_KERNEL
> >   	if (thumb) {
> > @@ -218,7 +218,7 @@ prepare_emulated_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
> >    */
> >   static void  __kprobes
> >   set_emulated_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
> > -								bool thumb)
> > +			bool thumb)
>
> Another spurious whitespace change.

Fixed.

> >   {
> >   #ifdef CONFIG_THUMB2_KERNEL
> >   	if (thumb) {
> > @@ -253,7 +253,7 @@ set_emulated_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
> >    * non-zero value, the corresponding nibble in pinsn is validated and modified
> >    * according to the type.
> >    */
> > -static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs)
> > +static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs, bool modify)
> >   {
> >   	probes_opcode_t insn = *pinsn;
> >   	probes_opcode_t mask = 0xf; /* Start at least significant nibble */
> > @@ -317,9 +317,16 @@ static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs)
> >   		/* Replace value of nibble with new register number... */
> >   		insn &= ~mask;
> >   		insn |= new_bits & mask;
> > +		if (modify) {
> > +			/* Replace value of nibble with new register number */
> > +			insn &= ~mask;
> > +			insn |= new_bits & mask;
> > +		}
>
> Huh? As is, the above addition doesn't do anything because insn has
> already been modified. I guess you played with the idea that you needed
> to avoid changing insn (you don't) and then didn't undo the experiment
> quite right. :-)

The conditional modification of the instruction was part of Rabin's 
original work for uprobes, but I messed up the merge from an earlier 
working version of my patches.  My intention was/is to delete the old 
unconditional code.  Sounds like maybe you disagree though.  The intent 
is to only modify the instruction in the kprobes case.

> >   	}
> >
> > -	*pinsn = insn;
> > +	if (modify)
> > +		*pinsn = insn;
> > +
> >   	return true;
> >
> >   reject:
> > @@ -380,14 +387,15 @@ static const int decode_struct_sizes[NUM_DECODE_TYPES] = {
> >    */
> >   int __kprobes
> >   probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
> > -				const union decode_item *table, bool thumb,
> > -				const union decode_item *actions)
> > +		   const union decode_item *table, bool thumb,
> > +		   bool emulate, const union decode_item *actions)
> >   {
> >   	struct decode_header *h = (struct decode_header *)table;
> >   	struct decode_header *next;
> >   	bool matched = false;
> >
> > -	insn = prepare_emulated_insn(insn, asi, thumb);
> > +	if (emulate)
> > +		insn = prepare_emulated_insn(insn, asi, thumb);
> >
> >   	for (;; h = next) {
> >   		enum decode_type type = h->type_regs.bits & DECODE_TYPE_MASK;
> > @@ -402,7 +410,7 @@ probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
> >   		if (!matched && (insn & h->mask.bits) != h->value.bits)
> >   			continue;
> >
> > -		if (!decode_regs(&insn, regs))
> > +		if (!decode_regs(&insn, regs, emulate))
> >   			return INSN_REJECTED;
> >
> >   		switch (type) {
> > @@ -415,7 +423,8 @@ probes_decode_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
> >
> >   		case DECODE_TYPE_CUSTOM: {
> >   			struct decode_custom *d = (struct decode_custom *)h;
> > -			return actions[d->decoder.bits].decoder(insn, asi, h);
> > +			return actions[d->decoder.bits].decoder(insn,
> > +					asi, h);
>
> No need to split the above line, you haven't changed it and it doesn't
> exceed 80 characters anyway.

Fixed.

> [Rest of patch cut]

-dl

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