From cd0ea35ff5511cde299a61c21a95889b4a71464e Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Fri, 12 Feb 2016 13:02:12 -0800 Subject: signals, pkeys: Notify userspace about protection key faults A protection key fault is very similar to any other access error. There must be a VMA, etc... We even want to take the same action (SIGSEGV) that we do with a normal access fault. However, we do need to let userspace know that something is different. We do this the same way what we did with SEGV_BNDERR with Memory Protection eXtensions (MPX): define a new SEGV code: SEGV_PKUERR. We add a siginfo field: si_pkey that reveals to userspace which protection key was set on the PTE that we faulted on. There is no other easy way for userspace to figure this out. They could parse smaps but that would be a bit cruel. We share space with in siginfo with _addr_bnd. #BR faults from MPX are completely separate from page faults (#PF) that trigger from protection key violations, so we never need both at the same time. Note that _pkey is a 64-bit value. The current hardware only supports 4-bit protection keys. We do this because there is _plenty_ of space in _sigfault and it is possible that future processors would support more than 4 bits of protection keys. The x86 code to actually fill in the siginfo is in the next patch. Signed-off-by: Dave Hansen Reviewed-by: Thomas Gleixner Cc: Al Viro Cc: Amanieu d'Antras Cc: Andrew Morton Cc: Andy Lutomirski Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Palmer Dabbelt Cc: Peter Zijlstra Cc: Richard Weinberger Cc: Rik van Riel Cc: Sasha Levin Cc: Vegard Nossum Cc: Vladimir Davydov Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20160212210212.3A9B83AC@viggo.jf.intel.com Signed-off-by: Ingo Molnar --- include/uapi/asm-generic/siginfo.h | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) (limited to 'include/uapi/asm-generic') diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h index 1e3552037a5a..90384d55225b 100644 --- a/include/uapi/asm-generic/siginfo.h +++ b/include/uapi/asm-generic/siginfo.h @@ -91,10 +91,15 @@ typedef struct siginfo { int _trapno; /* TRAP # which caused the signal */ #endif short _addr_lsb; /* LSB of the reported address */ - struct { - void __user *_lower; - void __user *_upper; - } _addr_bnd; + union { + /* used when si_code=SEGV_BNDERR */ + struct { + void __user *_lower; + void __user *_upper; + } _addr_bnd; + /* used when si_code=SEGV_PKUERR */ + u64 _pkey; + }; } _sigfault; /* SIGPOLL */ @@ -137,6 +142,7 @@ typedef struct siginfo { #define si_addr_lsb _sifields._sigfault._addr_lsb #define si_lower _sifields._sigfault._addr_bnd._lower #define si_upper _sifields._sigfault._addr_bnd._upper +#define si_pkey _sifields._sigfault._pkey #define si_band _sifields._sigpoll._band #define si_fd _sifields._sigpoll._fd #ifdef __ARCH_SIGSYS @@ -206,7 +212,8 @@ typedef struct siginfo { #define SEGV_MAPERR (__SI_FAULT|1) /* address not mapped to object */ #define SEGV_ACCERR (__SI_FAULT|2) /* invalid permissions for mapped object */ #define SEGV_BNDERR (__SI_FAULT|3) /* failed address bound checks */ -#define NSIGSEGV 3 +#define SEGV_PKUERR (__SI_FAULT|4) /* failed protection key checks */ +#define NSIGSEGV 4 /* * SIGBUS si_codes -- cgit v1.2.3 From 49cd53bf14aeb471c4a2682300dfc05ef2fd09f2 Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Tue, 1 Mar 2016 04:54:51 -0800 Subject: mm/pkeys: Fix siginfo ABI breakage caused by new u64 field Stephen Rothwell reported this linux-next build failure: http://lkml.kernel.org/r/20160226164406.065a1ffc@canb.auug.org.au ... caused by the Memory Protection Keys patches from the tip tree triggering a newly introduced build-time sanity check on an ARM build, because they changed the ABI of siginfo in an unexpected way. If u64 has a natural alignment of 8 bytes (which is the case on most mainstream platforms, with the notable exception of x86-32), then the leadup to the _sifields union matters: typedef struct siginfo { int si_signo; int si_errno; int si_code; union { ... } _sifields; } __ARCH_SI_ATTRIBUTES siginfo_t; Note how the first 3 fields give us 12 bytes, so _sifields is not 8 naturally bytes aligned. Before the _pkey field addition the largest element of _sifields (on 32-bit platforms) was 32 bits. With the u64 added, the minimum alignment requirement increased to 8 bytes on those (rare) 32-bit platforms. Thus GCC padded the space after si_code with 4 extra bytes, and shifted all _sifields offsets by 4 bytes - breaking the ABI of all of those remaining fields. On 64-bit platforms this problem was hidden due to _sifields already having numerous fields with natural 8 bytes alignment (pointers). To fix this, we replace the u64 with an '__u32'. The __u32 does not increase the minimum alignment requirement of the union, and it is also large enough to store the 16-bit pkey we have today on x86. Reported-by: Stehen Rothwell Signed-off-by: Dave Hansen Acked-by: Stehen Rothwell Cc: Andrew Morton Cc: Dave Hansen Cc: Helge Deller Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-next@vger.kernel.org Fixes: cd0ea35ff551 ("signals, pkeys: Notify userspace about protection key faults") Link: http://lkml.kernel.org/r/20160301125451.02C7426D@viggo.jf.intel.com Signed-off-by: Ingo Molnar --- include/uapi/asm-generic/siginfo.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/uapi/asm-generic') diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h index 90384d55225b..1abaf62c86fc 100644 --- a/include/uapi/asm-generic/siginfo.h +++ b/include/uapi/asm-generic/siginfo.h @@ -98,7 +98,7 @@ typedef struct siginfo { void __user *_upper; } _addr_bnd; /* used when si_code=SEGV_PKUERR */ - u64 _pkey; + __u32 _pkey; }; } _sigfault; -- cgit v1.2.3