On Wed, Aug 29, 2018 at 9:10 AM Borislav Petkov <b...@suse.de> wrote:
>
> On Tue, Aug 28, 2018 at 05:49:01PM +0200, Jann Horn wrote:
> > show_opcodes() is used both for dumping kernel instructions and for dumping
> > user instructions. If userspace causes #PF by jumping to a kernel address,
> > show_opcodes() can be reached with regs->ip controlled by the user,
> > pointing to kernel code. Make sure that userspace can't trick us into
> > dumping kernel memory into dmesg.
> >
> > Cc: sta...@vger.kernel.org
> > Fixes: 7cccf0725cf7 ("x86/dumpstack: Add a show_ip() function")
> > Reviewed-by: Kees Cook <keesc...@chromium.org>
> > Signed-off-by: Jann Horn <ja...@google.com>
> > ---
> > v2: Andy pointed out that I probably shouldn't be doing wrapping
> > arithmetic on pointers.
> >
> > arch/x86/include/asm/stacktrace.h | 2 +-
> > arch/x86/kernel/dumpstack.c | 13 ++++++++++---
> > arch/x86/mm/fault.c | 2 +-
> > 3 files changed, 12 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/stacktrace.h
> > b/arch/x86/include/asm/stacktrace.h
> > index b6dc698f992a..f335aad404a4 100644
> > --- a/arch/x86/include/asm/stacktrace.h
> > +++ b/arch/x86/include/asm/stacktrace.h
> > @@ -111,6 +111,6 @@ static inline unsigned long caller_frame_pointer(void)
> > return (unsigned long)frame;
> > }
> >
> > -void show_opcodes(u8 *rip, const char *loglvl);
> > +void show_opcodes(struct pt_regs *regs, const char *loglvl);
> > void show_ip(struct pt_regs *regs, const char *loglvl);
> > #endif /* _ASM_X86_STACKTRACE_H */
> > diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> > index 9c8652974f8e..14b337582b6f 100644
> > --- a/arch/x86/kernel/dumpstack.c
> > +++ b/arch/x86/kernel/dumpstack.c
> > @@ -89,14 +89,21 @@ static void printk_stack_address(unsigned long address,
> > int reliable,
> > * Thus, the 2/3rds prologue and 64 byte OPCODE_BUFSIZE is just a random
> > * guesstimate in attempt to achieve all of the above.
> > */
> > -void show_opcodes(u8 *rip, const char *loglvl)
> > +void show_opcodes(struct pt_regs *regs, const char *loglvl)
> > {
> > #define PROLOGUE_SIZE 42
> > #define EPILOGUE_SIZE 21
> > #define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)
> > u8 opcodes[OPCODE_BUFSIZE];
> > + u8 *prologue = (u8 *)(regs->ip - PROLOGUE_SIZE);
>
> Just a nitpick:
>
> <--- newline here.
The code below this point is still part of the declarations. Do you
want a newline here anyway? If you say yes, I'll adjust and resend.
> > + /*
> > + * Make sure userspace isn't trying to trick us into dumping kernel
> > + * memory by pointing the userspace instruction pointer at it.
> > + */
> > + bool bad_ip = user_mode(regs) &&
> > + __range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);
>
> Other than that:
>
> Reviewed-by: Borislav Petkov <b...@suse.de>
>
> Thx.
>
> --
> Regards/Gruss,
> Boris.
>
> SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB
> 21284 (AG Nürnberg)
> --
