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Groups > linux.kernel > #1346589 > unrolled thread
| Started by | Dave Hansen <dave@sr71.net> |
|---|---|
| First post | 2016-03-01 14:00 +0100 |
| Last post | 2016-03-03 18:30 +0100 |
| Articles | 4 — 4 participants |
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[PATCH] [v4] x86, pkeys: fix siginfo ABI breakage from new field Dave Hansen <dave@sr71.net> - 2016-03-01 14:00 +0100
Re: [PATCH] [v4] x86, pkeys: fix siginfo ABI breakage from new field Ingo Molnar <mingo@kernel.org> - 2016-03-03 16:50 +0100
[tip:mm/pkeys] mm/pkeys: Fix siginfo ABI breakage caused by new u64 field tip-bot for Dave Hansen <tipbot@zytor.com> - 2016-03-03 18:00 +0100
Re: [tip:mm/pkeys] mm/pkeys: Fix siginfo ABI breakage caused by new u64 field Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-03 18:30 +0100
| From | Dave Hansen <dave@sr71.net> |
|---|---|
| Date | 2016-03-01 14:00 +0100 |
| Subject | [PATCH] [v4] x86, pkeys: fix siginfo ABI breakage from new field |
| Message-ID | <r7S4b-Pg-23@gated-at.bofh.it> |
Update changelog with better description of the issue from Ingo.
--
From: Dave Hansen <dave.hansen@linux.intel.com>
Stephen Rothwell reported:
http://lkml.kernel.org/r/20160226164406.065a1ffc@canb.auug.org.au
that the Memory Protection Keys patches from the tip tree broke a
build-time check on an ARM build because they changed the ABI of
siginfo.
If u64 has a natural alignment of 8 bytes (this is rare, most 32-bit
platforms align it to 4 bytes), 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 is
guaranteed to union well with the pointers from _addr_bnd. It is also
plenty large enough to store the 16-bit pkey we have today on x86.
I also shouldn't have been using a u64 in a userspace API to begin with.
Fixes: cd0ea35ff551 ("signals, pkeys: Notify userspace about protection key faults")
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Stehen Rothwell <sfr@canb.auug.org.au>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-next@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Helge Deller <deller@gmx.de>
---
b/arch/ia64/include/uapi/asm/siginfo.h | 2 +-
b/arch/mips/include/uapi/asm/siginfo.h | 2 +-
b/include/uapi/asm-generic/siginfo.h | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)
diff -puN include/uapi/asm-generic/siginfo.h~pkeys-101-fix-siginfo include/uapi/asm-generic/siginfo.h
--- a/include/uapi/asm-generic/siginfo.h~pkeys-101-fix-siginfo 2016-02-29 09:22:45.327228965 -0800
+++ b/include/uapi/asm-generic/siginfo.h 2016-02-29 09:22:45.333229241 -0800
@@ -98,7 +98,7 @@ typedef struct siginfo {
void __user *_upper;
} _addr_bnd;
/* used when si_code=SEGV_PKUERR */
- u64 _pkey;
+ __u32 _pkey;
};
} _sigfault;
diff -puN arch/mips/include/uapi/asm/siginfo.h~pkeys-101-fix-siginfo arch/mips/include/uapi/asm/siginfo.h
--- a/arch/mips/include/uapi/asm/siginfo.h~pkeys-101-fix-siginfo 2016-02-29 09:22:45.330229103 -0800
+++ b/arch/mips/include/uapi/asm/siginfo.h 2016-02-29 09:22:45.333229241 -0800
@@ -93,7 +93,7 @@ typedef struct siginfo {
void __user *_upper;
} _addr_bnd;
/* used when si_code=SEGV_PKUERR */
- u64 _pkey;
+ __u32 _pkey;
};
} _sigfault;
diff -puN arch/ia64/include/uapi/asm/siginfo.h~pkeys-101-fix-siginfo arch/ia64/include/uapi/asm/siginfo.h
--- a/arch/ia64/include/uapi/asm/siginfo.h~pkeys-101-fix-siginfo 2016-02-29 09:22:45.331229149 -0800
+++ b/arch/ia64/include/uapi/asm/siginfo.h 2016-02-29 09:22:45.333229241 -0800
@@ -70,7 +70,7 @@ typedef struct siginfo {
void __user *_upper;
} _addr_bnd;
/* used when si_code=SEGV_PKUERR */
- u64 _pkey;
+ __u32 _pkey;
};
} _sigfault;
_
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| From | Ingo Molnar <mingo@kernel.org> |
|---|---|
| Date | 2016-03-03 16:50 +0100 |
| Message-ID | <r8DFN-IC-15@gated-at.bofh.it> |
| In reply to | #1346589 |
* Dave Hansen <dave@sr71.net> wrote: > To fix this, we replace the u64 with an '__u32'. The __u32 is guaranteed to > union well with the pointers from _addr_bnd. It is also plenty large enough to > store the 16-bit pkey we have today on x86. The 'union well' sentence is really a leftover from the earlier changelog (the problem was never about interaction between union members) - a better explantion is: > To fix this, we replace the u64 with an '__u32'. The __u32 does not change the > minimum alignment requirements of the structure and it is also plenty large > enough to store the 16-bit pkey we have today on x86. I fixed this up locally, no need to resend. Thanks, Ingo
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| From | tip-bot for Dave Hansen <tipbot@zytor.com> |
|---|---|
| Date | 2016-03-03 18:00 +0100 |
| Subject | [tip:mm/pkeys] mm/pkeys: Fix siginfo ABI breakage caused by new u64 field |
| Message-ID | <r8ELx-1ze-43@gated-at.bofh.it> |
| In reply to | #1346589 |
Commit-ID: 16bc7477807393efb5b81f875888ee9221ead3a1
Gitweb: http://git.kernel.org/tip/16bc7477807393efb5b81f875888ee9221ead3a1
Author: Dave Hansen <dave.hansen@linux.intel.com>
AuthorDate: Tue, 1 Mar 2016 04:54:51 -0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 3 Mar 2016 16:44:21 +0100
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 (this is rare, most 32-bit
platforms align it to 4 bytes), 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 <sfr@canb.auug.org.au>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Stehen Rothwell <sfr@canb.auug.org.au>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave@sr71.net>
Cc: Helge Deller <deller@gmx.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
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 <mingo@kernel.org>
---
arch/ia64/include/uapi/asm/siginfo.h | 2 +-
arch/mips/include/uapi/asm/siginfo.h | 2 +-
include/uapi/asm-generic/siginfo.h | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/ia64/include/uapi/asm/siginfo.h b/arch/ia64/include/uapi/asm/siginfo.h
index 0151cfa..f72bf01 100644
--- a/arch/ia64/include/uapi/asm/siginfo.h
+++ b/arch/ia64/include/uapi/asm/siginfo.h
@@ -70,7 +70,7 @@ typedef struct siginfo {
void __user *_upper;
} _addr_bnd;
/* used when si_code=SEGV_PKUERR */
- u64 _pkey;
+ __u32 _pkey;
};
} _sigfault;
diff --git a/arch/mips/include/uapi/asm/siginfo.h b/arch/mips/include/uapi/asm/siginfo.h
index 6f4edf0..cc49dc2 100644
--- a/arch/mips/include/uapi/asm/siginfo.h
+++ b/arch/mips/include/uapi/asm/siginfo.h
@@ -93,7 +93,7 @@ typedef struct siginfo {
void __user *_upper;
} _addr_bnd;
/* used when si_code=SEGV_PKUERR */
- u64 _pkey;
+ __u32 _pkey;
};
} _sigfault;
diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
index 90384d5..1abaf62 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;
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| From | Linus Torvalds <torvalds@linux-foundation.org> |
|---|---|
| Date | 2016-03-03 18:30 +0100 |
| Subject | Re: [tip:mm/pkeys] mm/pkeys: Fix siginfo ABI breakage caused by new u64 field |
| Message-ID | <r8Fez-21e-31@gated-at.bofh.it> |
| In reply to | #1349373 |
On Thu, Mar 3, 2016 at 8:53 AM, tip-bot for Dave Hansen
<tipbot@zytor.com> wrote:
>
> If u64 has a natural alignment of 8 bytes (this is rare, most 32-bit
> platforms align it to 4 bytes), then the leadup to the _sifields union
> matters:
Side note: I'm not sure that "this is rare" comment is necessarily correct.
I think natural alignment is pretty common, even for 32-bit targets.
x86-32 is I think the exception rather than the rule.
There is some real odd case iirc - embedded m68k, which has some
ridiculous alignment rules. I think it only ever aligns to 16-bit
boundaries.
I do keep coming back to the fact that we should *probably* just do
something like
typedef unsigned long long __attribute__((aligned(8))) __u64;
and then introduce a separate "u64_unaligned" type for all the legacy
cases that depended on 32-bit alignment.
It's horrendously nasty to test, though.
Linus
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