Re: [PATCH 1/6] x86/KASLR: make getting random long number function public

[joeyli <jlee@suse.com>]

Hi Ard,

On Sun, Aug 05, 2018 at 10:16:03AM +0200, Ard Biesheuvel wrote:
> On 5 August 2018 at 05:21, Lee, Chun-Yi <joeyli.kernel@gmail.com> wrote:
> > Separating the functions for getting random long number from KASLR
> > to x86 library, then it can be used to generate random long for
> > EFI root key.
> >
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> > Cc: Pavel Machek <pavel@ucw.cz>
> > Cc: Chen Yu <yu.c.chen@intel.com>
> > Cc: Oliver Neukum <oneukum@suse.com>
> > Cc: Ryan Chen <yu.chen.surf@gmail.com>
> > Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > Cc: David Howells <dhowells@redhat.com>
> > Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
> > Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
> 
> Not my call to make perhaps, but i'm nacking it anyway.
> 
> Playing games with counters and other low entropy inputs may have been
> acceptable for kaslr on x86 when it was first introduced, but using it
> to generate symmetric keys is really out of the question.
> 
> On modern x86, i suppose rdrand is a given, and these days we have
> EFI_RNG_PROTOCOL as well (and an open source UEFI driver for ChasoKey,
> btw - perhaps we should try and get MS to sign that?), although I'm
> not sure whether any x86 support this out of the box now.
> 
> BTW using low entropy inputs on top of rdrand or EFI_RNG_PROTOCOL is
> fine, if you're paranoid, but if you have neither of those, you should
> really fail the call.
> 

I agreed with your suggestion. I will add EFI_RNG_PROTOCOL and also checking
the existence of RDRAND and EFI_RNG_PROTOCOL.

Thanks for your view.

Joey Lee
 
> > ---
> >  arch/x86/boot/compressed/kaslr.c | 21 -------------
> >  arch/x86/boot/compressed/misc.c  | 17 ++++++++++
> >  arch/x86/boot/compressed/misc.h  |  6 ++++
> >  arch/x86/lib/kaslr.c             | 61 ++---------------------------------
> >  arch/x86/lib/random.c            | 68 ++++++++++++++++++++++++++++++++++++++++
> >  5 files changed, 93 insertions(+), 80 deletions(-)
> >  create mode 100644 arch/x86/lib/random.c
> >
> > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> > index b87a7582853d..0f40d2178ebc 100644
> > --- a/arch/x86/boot/compressed/kaslr.c
> > +++ b/arch/x86/boot/compressed/kaslr.c
> > @@ -33,13 +33,11 @@
> >  #include "error.h"
> >  #include "../string.h"
> >
> > -#include <generated/compile.h>
> >  #include <linux/module.h>
> >  #include <linux/uts.h>
> >  #include <linux/utsname.h>
> >  #include <linux/ctype.h>
> >  #include <linux/efi.h>
> > -#include <generated/utsrelease.h>
> >  #include <asm/efi.h>
> >
> >  /* Macros used by the included decompressor code below. */
> > @@ -57,25 +55,6 @@ extern unsigned long get_cmd_line_ptr(void);
> >  /* Used by PAGE_KERN* macros: */
> >  pteval_t __default_kernel_pte_mask __read_mostly = ~0;
> >
> > -/* Simplified build-specific string for starting entropy. */
> > -static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
> > -               LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
> > -
> > -static unsigned long rotate_xor(unsigned long hash, const void *area,
> > -                               size_t size)
> > -{
> > -       size_t i;
> > -       unsigned long *ptr = (unsigned long *)area;
> > -
> > -       for (i = 0; i < size / sizeof(hash); i++) {
> > -               /* Rotate by odd number of bits and XOR. */
> > -               hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
> > -               hash ^= ptr[i];
> > -       }
> > -
> > -       return hash;
> > -}
> > -
> >  /* Attempt to create a simple but unpredictable starting entropy. */
> >  static unsigned long get_boot_seed(void)
> >  {
> > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> > index 8dd1d5ccae58..eb0ab9cad4e4 100644
> > --- a/arch/x86/boot/compressed/misc.c
> > +++ b/arch/x86/boot/compressed/misc.c
> > @@ -426,3 +426,20 @@ void fortify_panic(const char *name)
> >  {
> >         error("detected buffer overflow");
> >  }
> > +
> > +#if CONFIG_RANDOMIZE_BASE
> > +unsigned long rotate_xor(unsigned long hash, const void *area,
> > +                       size_t size)
> > +{
> > +       size_t i;
> > +       unsigned long *ptr = (unsigned long *)area;
> > +
> > +       for (i = 0; i < size / sizeof(hash); i++) {
> > +               /* Rotate by odd number of bits and XOR. */
> > +               hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
> > +               hash ^= ptr[i];
> > +       }
> > +
> > +       return hash;
> > +}
> > +#endif
> > diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> > index a423bdb42686..957f327ad83c 100644
> > --- a/arch/x86/boot/compressed/misc.h
> > +++ b/arch/x86/boot/compressed/misc.h
> > @@ -70,6 +70,8 @@ int cmdline_find_option_bool(const char *option);
> >
> >
> >  #if CONFIG_RANDOMIZE_BASE
> > +#include <generated/compile.h>
> > +#include <generated/utsrelease.h>
> >  /* kaslr.c */
> >  void choose_random_location(unsigned long input,
> >                             unsigned long input_size,
> > @@ -78,6 +80,10 @@ void choose_random_location(unsigned long input,
> >                             unsigned long *virt_addr);
> >  /* cpuflags.c */
> >  bool has_cpuflag(int flag);
> > +/* Simplified build-specific string for starting entropy. */
> > +static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
> > +               LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
> > +unsigned long rotate_xor(unsigned long hash, const void *area, size_t size);
> >  #else
> >  static inline void choose_random_location(unsigned long input,
> >                                           unsigned long input_size,
> > diff --git a/arch/x86/lib/kaslr.c b/arch/x86/lib/kaslr.c
> > index 79778ab200e4..29ed9bfde5a5 100644
> > --- a/arch/x86/lib/kaslr.c
> > +++ b/arch/x86/lib/kaslr.c
> > @@ -26,67 +26,10 @@
> >  #define get_boot_seed() kaslr_offset()
> >  #endif
> >
> > -#define I8254_PORT_CONTROL     0x43
> > -#define I8254_PORT_COUNTER0    0x40
> > -#define I8254_CMD_READBACK     0xC0
> > -#define I8254_SELECT_COUNTER0  0x02
> > -#define I8254_STATUS_NOTREADY  0x40
> > -static inline u16 i8254(void)
> > -{
> > -       u16 status, timer;
> > -
> > -       do {
> > -               outb(I8254_PORT_CONTROL,
> > -                    I8254_CMD_READBACK | I8254_SELECT_COUNTER0);
> > -               status = inb(I8254_PORT_COUNTER0);
> > -               timer  = inb(I8254_PORT_COUNTER0);
> > -               timer |= inb(I8254_PORT_COUNTER0) << 8;
> > -       } while (status & I8254_STATUS_NOTREADY);
> > -
> > -       return timer;
> > -}
> > +#include "random.c"
> >
> >  unsigned long kaslr_get_random_long(const char *purpose)
> >  {
> > -#ifdef CONFIG_X86_64
> > -       const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
> > -#else
> > -       const unsigned long mix_const = 0x3f39e593UL;
> > -#endif
> > -       unsigned long raw, random = get_boot_seed();
> > -       bool use_i8254 = true;
> > -
> > -       debug_putstr(purpose);
> >         debug_putstr(" KASLR using");
> > -
> > -       if (has_cpuflag(X86_FEATURE_RDRAND)) {
> > -               debug_putstr(" RDRAND");
> > -               if (rdrand_long(&raw)) {
> > -                       random ^= raw;
> > -                       use_i8254 = false;
> > -               }
> > -       }
> > -
> > -       if (has_cpuflag(X86_FEATURE_TSC)) {
> > -               debug_putstr(" RDTSC");
> > -               raw = rdtsc();
> > -
> > -               random ^= raw;
> > -               use_i8254 = false;
> > -       }
> > -
> > -       if (use_i8254) {
> > -               debug_putstr(" i8254");
> > -               random ^= i8254();
> > -       }
> > -
> > -       /* Circular multiply for better bit diffusion */
> > -       asm(_ASM_MUL "%3"
> > -           : "=a" (random), "=d" (raw)
> > -           : "a" (random), "rm" (mix_const));
> > -       random += raw;
> > -
> > -       debug_putstr("...\n");
> > -
> > -       return random;
> > +       return get_random_long(purpose);
> >  }
> > diff --git a/arch/x86/lib/random.c b/arch/x86/lib/random.c
> > new file mode 100644
> > index 000000000000..f2fe6a784c98
> > --- /dev/null
> > +++ b/arch/x86/lib/random.c
> > @@ -0,0 +1,68 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <asm/io.h>
> > +#include <asm/archrandom.h>
> > +
> > +#define I8254_PORT_CONTROL     0x43
> > +#define I8254_PORT_COUNTER0    0x40
> > +#define I8254_CMD_READBACK     0xC0
> > +#define I8254_SELECT_COUNTER0  0x02
> > +#define I8254_STATUS_NOTREADY  0x40
> > +static inline u16 i8254(void)
> > +{
> > +       u16 status, timer;
> > +
> > +       do {
> > +               outb(I8254_PORT_CONTROL,
> > +                    I8254_CMD_READBACK | I8254_SELECT_COUNTER0);
> > +               status = inb(I8254_PORT_COUNTER0);
> > +               timer  = inb(I8254_PORT_COUNTER0);
> > +               timer |= inb(I8254_PORT_COUNTER0) << 8;
> > +       } while (status & I8254_STATUS_NOTREADY);
> > +
> > +       return timer;
> > +}
> > +
> > +static unsigned long get_random_long(const char *purpose)
> > +{
> > +#ifdef CONFIG_X86_64
> > +       const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
> > +#else
> > +       const unsigned long mix_const = 0x3f39e593UL;
> > +#endif
> > +       unsigned long raw, random = get_boot_seed();
> > +       bool use_i8254 = true;
> > +
> > +       debug_putstr(purpose);
> > +
> > +       if (has_cpuflag(X86_FEATURE_RDRAND)) {
> > +               debug_putstr(" RDRAND");
> > +               if (rdrand_long(&raw)) {
> > +                       random ^= raw;
> > +                       use_i8254 = false;
> > +               }
> > +       }
> > +
> > +       if (has_cpuflag(X86_FEATURE_TSC)) {
> > +               debug_putstr(" RDTSC");
> > +               raw = rdtsc();
> > +
> > +               random ^= raw;
> > +               use_i8254 = false;
> > +       }
> > +
> > +       if (use_i8254) {
> > +               debug_putstr(" i8254");
> > +               random ^= i8254();
> > +       }
> > +
> > +       /* Circular multiply for better bit diffusion */
> > +       asm(_ASM_MUL "%3"
> > +           : "=a" (random), "=d" (raw)
> > +           : "a" (random), "rm" (mix_const));
> > +       random += raw;
> > +
> > +       debug_putstr("...\n");
> > +
> > +       return random;
> > +}
> > --
> > 2.13.6
> >
> --
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