From df3735c5b40fad8d0d28eb8ab065fe955b3347ee Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Wed, 6 Sep 2017 16:25:11 -0700 Subject: x86,mpx: make mpx depend on x86-64 to free up VMA flag Patch series "mm,fork,security: introduce MADV_WIPEONFORK", v4. If a child process accesses memory that was MADV_WIPEONFORK, it will get zeroes. The address ranges are still valid, they are just empty. If a child process accesses memory that was MADV_DONTFORK, it will get a segmentation fault, since those address ranges are no longer valid in the child after fork. Since MADV_DONTFORK also seems to be used to allow very large programs to fork in systems with strict memory overcommit restrictions, changing the semantics of MADV_DONTFORK might break existing programs. The use case is libraries that store or cache information, and want to know that they need to regenerate it in the child process after fork. Examples of this would be: - systemd/pulseaudio API checks (fail after fork) (replacing a getpid check, which is too slow without a PID cache) - PKCS#11 API reinitialization check (mandated by specification) - glibc's upcoming PRNG (reseed after fork) - OpenSSL PRNG (reseed after fork) The security benefits of a forking server having a re-inialized PRNG in every child process are pretty obvious. However, due to libraries having all kinds of internal state, and programs getting compiled with many different versions of each library, it is unreasonable to expect calling programs to re-initialize everything manually after fork. A further complication is the proliferation of clone flags, programs bypassing glibc's functions to call clone directly, and programs calling unshare, causing the glibc pthread_atfork hook to not get called. It would be better to have the kernel take care of this automatically. The patchset also adds MADV_KEEPONFORK, to undo the effects of a prior MADV_WIPEONFORK. This is similar to the OpenBSD minherit syscall with MAP_INHERIT_ZERO: https://man.openbsd.org/minherit.2 This patch (of 2): MPX only seems to be available on 64 bit CPUs, starting with Skylake and Goldmont. Move VM_MPX into the 64 bit only portion of vma->vm_flags, in order to free up a VMA flag. Link: http://lkml.kernel.org/r/20170811212829.29186-2-riel@redhat.com Signed-off-by: Rik van Riel Acked-by: Dave Hansen Cc: Mike Kravetz Cc: Florian Weimer Cc: Kees Cook Cc: Andy Lutomirski Cc: Will Drewry Cc: Ingo Molnar Cc: Thomas Gleixner Cc: "H. Peter Anvin" Cc: "Kirill A. Shutemov" Cc: Matthew Wilcox Cc: Colm MacCártaigh Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/mm.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/mm.h b/include/linux/mm.h index 0acea73af839..9efe62032094 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -208,10 +208,12 @@ extern unsigned int kobjsize(const void *objp); #define VM_HIGH_ARCH_BIT_1 33 /* bit only usable on 64-bit architectures */ #define VM_HIGH_ARCH_BIT_2 34 /* bit only usable on 64-bit architectures */ #define VM_HIGH_ARCH_BIT_3 35 /* bit only usable on 64-bit architectures */ +#define VM_HIGH_ARCH_BIT_4 36 /* bit only usable on 64-bit architectures */ #define VM_HIGH_ARCH_0 BIT(VM_HIGH_ARCH_BIT_0) #define VM_HIGH_ARCH_1 BIT(VM_HIGH_ARCH_BIT_1) #define VM_HIGH_ARCH_2 BIT(VM_HIGH_ARCH_BIT_2) #define VM_HIGH_ARCH_3 BIT(VM_HIGH_ARCH_BIT_3) +#define VM_HIGH_ARCH_4 BIT(VM_HIGH_ARCH_BIT_4) #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */ #if defined(CONFIG_X86) @@ -235,9 +237,11 @@ extern unsigned int kobjsize(const void *objp); # define VM_MAPPED_COPY VM_ARCH_1 /* T if mapped copy of data (nommu mmap) */ #endif -#if defined(CONFIG_X86) +#if defined(CONFIG_X86_INTEL_MPX) /* MPX specific bounds table or bounds directory */ -# define VM_MPX VM_ARCH_2 +# define VM_MPX VM_HIGH_ARCH_BIT_4 +#else +# define VM_MPX VM_NONE #endif #ifndef VM_GROWSUP -- cgit v1.2.3