Messages in this thread | | | Subject | Re: [PATCH v25 30/30] mm: Introduce PROT_SHSTK for shadow stack | From | "Yu, Yu-cheng" <> | Date | Mon, 26 Apr 2021 11:00:58 -0700 |
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On 4/25/2021 11:52 PM, Kirill A. Shutemov wrote: > On Thu, Apr 15, 2021 at 03:14:19PM -0700, Yu-cheng Yu wrote: >> There are three possible options to create a shadow stack allocation API: >> an arch_prctl, a new syscall, or adding PROT_SHSTK to mmap()/mprotect(). >> Each has its advantages and compromises. >> >> An arch_prctl() is the least intrusive. However, the existing x86 >> arch_prctl() takes only two parameters. Multiple parameters must be >> passed in a memory buffer. There is a proposal to pass more parameters in >> registers [1], but no active discussion on that. >> >> A new syscall minimizes compatibility issues and offers an extensible frame >> work to other architectures, but this will likely result in some overlap of >> mmap()/mprotect(). >> >> The introduction of PROT_SHSTK to mmap()/mprotect() takes advantage of > > Maybe PROT_SHADOW_STACK? > >> existing APIs. The x86-specific PROT_SHSTK is translated to >> VM_SHADOW_STACK and a shadow stack mapping is created without reinventing >> the wheel. There are potential pitfalls though. The most obvious one >> would be using this as a bypass to shadow stack protection. However, the >> attacker would have to get to the syscall first. >> >> [1] https://lore.kernel.org/lkml/20200828121624.108243-1-hjl.tools@gmail.com/ >> >> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> >> Cc: Kees Cook <keescook@chromium.org> >> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> >> --- >> v24: >> - Update arch_calc_vm_prot_bits(), leave PROT* checking to >> arch_validate_prot(). >> - Update arch_validate_prot(), leave vma flags checking to >> arch_validate_flags(). >> - Add arch_validate_flags(). >> >> arch/x86/include/asm/mman.h | 59 +++++++++++++++++++++++++++++++- >> arch/x86/include/uapi/asm/mman.h | 1 + >> include/linux/mm.h | 1 + >> 3 files changed, 60 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/include/asm/mman.h b/arch/x86/include/asm/mman.h >> index 629f6c81263a..1821c179f35d 100644 >> --- a/arch/x86/include/asm/mman.h >> +++ b/arch/x86/include/asm/mman.h
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>> + >> +#define arch_validate_prot arch_validate_prot >> + >> +static inline bool arch_validate_flags(unsigned long vm_flags, bool is_anon) >> +{ >> + if (vm_flags & VM_SHADOW_STACK) { >> + if ((vm_flags & VM_SHARED) || !is_anon) > > VM_SHARED check is redundant. vma_is_anonymous() should be enough. > Anonymous shared mappings would fail vma_is_anonymous(). >
Thanks for looking into this. I will update and send another version.
Yu-cheng
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