| Message ID | 20200205181935.3712-19-yu-cheng.yu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Control-flow Enforcement: Shadow Stack | expand |
On Wed, Feb 05, 2020 at 10:19:26AM -0800, Yu-cheng Yu wrote: > WRUSS is a new kernel-mode instruction but writes directly to user Shadow > Stack (SHSTK) memory. This is used to construct a return address on SHSTK > for the signal handler. > > This instruction can fault if the user SHSTK is not valid SHSTK memory. > In that case, the kernel does a fixup. Since these functions aren't used in this patch, should this get merged with patch 19? -Kees > > v4: > - Change to asm goto. > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> > --- > arch/x86/include/asm/special_insns.h | 32 ++++++++++++++++++++++++++++ > 1 file changed, 32 insertions(+) > > diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h > index 6d37b8fcfc77..1b9b2e79c353 100644 > --- a/arch/x86/include/asm/special_insns.h > +++ b/arch/x86/include/asm/special_insns.h > @@ -222,6 +222,38 @@ static inline void clwb(volatile void *__p) > : [pax] "a" (p)); > } > > +#ifdef CONFIG_X86_INTEL_CET > +#if defined(CONFIG_IA32_EMULATION) || defined(CONFIG_X86_X32) > +static inline int write_user_shstk_32(unsigned long addr, unsigned int val) > +{ > + asm_volatile_goto("1: wrussd %1, (%0)\n" > + _ASM_EXTABLE(1b, %l[fail]) > + :: "r" (addr), "r" (val) > + :: fail); > + return 0; > +fail: > + return -EPERM; > +} > +#else > +static inline int write_user_shstk_32(unsigned long addr, unsigned int val) > +{ > + WARN_ONCE(1, "%s used but not supported.\n", __func__); > + return -EFAULT; > +} > +#endif > + > +static inline int write_user_shstk_64(unsigned long addr, unsigned long val) > +{ > + asm_volatile_goto("1: wrussq %1, (%0)\n" > + _ASM_EXTABLE(1b, %l[fail]) > + :: "r" (addr), "r" (val) > + :: fail); > + return 0; > +fail: > + return -EPERM; > +} > +#endif /* CONFIG_X86_INTEL_CET */ > + > #define nop() asm volatile ("nop") > > > -- > 2.21.0 >
On Tue, 2020-02-25 at 13:10 -0800, Kees Cook wrote: > On Wed, Feb 05, 2020 at 10:19:26AM -0800, Yu-cheng Yu wrote: > > WRUSS is a new kernel-mode instruction but writes directly to user Shadow > > Stack (SHSTK) memory. This is used to construct a return address on SHSTK > > for the signal handler. > > > > This instruction can fault if the user SHSTK is not valid SHSTK memory. > > In that case, the kernel does a fixup. > > Since these functions aren't used in this patch, should this get merged > with patch 19? Yes, I can do that. Yu-cheng
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index 6d37b8fcfc77..1b9b2e79c353 100644 --- a/arch/x86/include/asm/special_insns.h +++ b/arch/x86/include/asm/special_insns.h @@ -222,6 +222,38 @@ static inline void clwb(volatile void *__p) : [pax] "a" (p)); } +#ifdef CONFIG_X86_INTEL_CET +#if defined(CONFIG_IA32_EMULATION) || defined(CONFIG_X86_X32) +static inline int write_user_shstk_32(unsigned long addr, unsigned int val) +{ + asm_volatile_goto("1: wrussd %1, (%0)\n" + _ASM_EXTABLE(1b, %l[fail]) + :: "r" (addr), "r" (val) + :: fail); + return 0; +fail: + return -EPERM; +} +#else +static inline int write_user_shstk_32(unsigned long addr, unsigned int val) +{ + WARN_ONCE(1, "%s used but not supported.\n", __func__); + return -EFAULT; +} +#endif + +static inline int write_user_shstk_64(unsigned long addr, unsigned long val) +{ + asm_volatile_goto("1: wrussq %1, (%0)\n" + _ASM_EXTABLE(1b, %l[fail]) + :: "r" (addr), "r" (val) + :: fail); + return 0; +fail: + return -EPERM; +} +#endif /* CONFIG_X86_INTEL_CET */ + #define nop() asm volatile ("nop")
WRUSS is a new kernel-mode instruction but writes directly to user Shadow Stack (SHSTK) memory. This is used to construct a return address on SHSTK for the signal handler. This instruction can fault if the user SHSTK is not valid SHSTK memory. In that case, the kernel does a fixup. v4: - Change to asm goto. Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> --- arch/x86/include/asm/special_insns.h | 32 ++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+)