On Fri, 12 Oct 2018 15:54:39 -0400 Steven Rostedt <rost...@goodmis.org> wrote:
> On Fri, 12 Oct 2018 11:21:28 -0700 > Andy Lutomirski <l...@amacapital.net> wrote: > > > On Fri, Oct 12, 2018 at 9:26 AM Steven Rostedt <rost...@goodmis.org> wrote: > > > > > > > > > Anyone have any issues with this patch? > > > > > > > I'm conceptually okay with it. That being said, > > regs_within_kernel_stack(), which you're indirectly using, is > > off-by-a-few. And updating it to use probe_kernel_read() might be > > nice for robustness. > > > > Something like this? > > -- Steve > > From: "Steven Rostedt (VMware)" <rost...@goodmis.org> > Date: Fri, 12 Oct 2018 15:44:20 -0400 > Subject: [PATCH] x86: ptrace.h: Add regs_get_kernel_stack_nth_safe() function > > Andy had some concerns about using regs_get_kernel_stack_nth() in a new > function regs_get_kernel_argument() as if there's any error in the stack > code, it could cause a bad memory access. Instead, add a new function called > regs_get_kernel_stack_nth_safe() that does a probe_kernel_read() on the > stack address to be extra careful in accessing the memory. To share the > code, regs_get_kernel_stack_nth_addr() was added to just return the stack > address (or NULL if not on the stack), that both regs_get_kernel_stack_nth() > and the _safe() version can use. This patch looks good to me. But if the concern is real, all regs_get_kernel_stack_nth() user must move onto _safe() version, at least all tracers code. Reviewed-by: Masami Hiramatsu <mhira...@kernel.org> Thanks, > > Link: > http://lkml.kernel.org/r/calcetrxn9zktb9i1lp3qofcpqzhf34bdkuz5d3n0ucmrr+v...@mail.gmail.com > Requested-by: Andy Lutomirski <l...@amacapital.net> > Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org> > --- > arch/x86/include/asm/ptrace.h | 57 > ++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 54 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h > index c2304b25e2fd..8df7ab6a17c5 100644 > --- a/arch/x86/include/asm/ptrace.h > +++ b/arch/x86/include/asm/ptrace.h > @@ -237,6 +237,27 @@ static inline int regs_within_kernel_stack(struct > pt_regs *regs, > } > > /** > + * regs_get_kernel_stack_nth_addr() - get the address of the Nth entry on > stack > + * @regs: pt_regs which contains kernel stack pointer. > + * @n: stack entry number. > + * > + * regs_get_kernel_stack_nth() returns the address of the @n th entry of the > + * kernel stack which is specified by @regs. If the @n th entry is NOT in > + * the kernel stack, this returns NULL. > + */ > +static inline unsigned long *regs_get_kernel_stack_nth_addr(struct pt_regs > *regs, > + unsigned int n) > +{ > + unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs); > + > + addr += n; > + if (regs_within_kernel_stack(regs, (unsigned long)addr)) > + return addr; > + else > + return NULL; > +} > + > +/** > * regs_get_kernel_stack_nth() - get Nth entry of the stack > * @regs: pt_regs which contains kernel stack pointer. > * @n: stack entry number. > @@ -248,14 +269,44 @@ static inline int regs_within_kernel_stack(struct > pt_regs *regs, > static inline unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, > unsigned int n) > { > - unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs); > - addr += n; > - if (regs_within_kernel_stack(regs, (unsigned long)addr)) > + unsigned long *addr; > + > + addr = regs_get_kernel_stack_nth_addr(regs, n); > + if (addr) > return *addr; > else > return 0; > } > > +/* To avoid include hell, we can't include uaccess.h */ > +extern long probe_kernel_read(void *dst, const void *src, size_t size); > + > +/** > + * regs_get_kernel_stack_nth_safe() - safely get Nth entry of the stack > + * @regs: pt_regs which contains kernel stack pointer. > + * @n: stack entry number. > + * > + * Same as regs_get_kernel_stack_nth(), but references the stack value > + * with a probe_kernel_read() in case there's a bad stack pointer, it > + * will not cause a bad memory access. If the @n is not on the stack, > + * or a bad memory access happened, it returns zero. > + */ > +static inline unsigned long regs_get_kernel_stack_nth_safe(struct pt_regs > *regs, > + unsigned int n) > +{ > + unsigned long *addr; > + unsigned long val; > + long ret; > + > + addr = regs_get_kernel_stack_nth_addr(regs, n); > + if (addr) { > + ret = probe_kernel_read(&val, addr, sizeof(val)); > + if (!ret) > + return val; > + } > + return 0; > +} > + > /** > * regs_get_kernel_argument() - get Nth function argument in kernel > * @regs: pt_regs of that context > -- > 2.13.6 > -- Masami Hiramatsu <mhira...@kernel.org>
