kernel/linux
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ synced 2026-10-18 19:12:56 +00:00
Code Issues Releases Packages Activity
No description
1,081,037 commits 116 branches 5,798 tags 5.6 GiB
  • C 96.9%
  • Assembly 0.9%
  • Rust 0.6%
  • Shell 0.6%
  • Python 0.5%
  • Other 0.3%
Find a file
Matt Turner f55e039ce8 alpha: don't leak hardware-fabricated FP exception bits to user space 
commit bcfe318741 upstream.

On EV6 and later the hardware records exception status bits in the FPCR
before delivering a software completion trap, and those bits can be wrong
for the instruction that trapped.  Converting a double that is exactly
representable as a subnormal float sets FPCR_UNF even though the result
is exact, and an underflow trap additionally sets FPCR_INE even when the
emulated operation turns out to be exact.

alpha_fp_emul() only wrote the FPCR when soft-fp raised an exception, so
whenever it determined that the instruction was exact the fabricated bits
stayed in the FPCR and were reported to user space by fetestexcept().

Pass the exception summary register down from do_entArith() so the
handler can tell which exceptions the hardware attributed to the trapping
instruction, and always write the FPCR.  Clear the exceptions that the
trap reported but that soft-fp did not raise.  EXC_SUM reports only the
underflow or overflow when the hardware also set INE, so treat INE as a
candidate in that case, and treat a trap with no reported exception as a
denormal operand trap, for which the hardware can fabricate INE and UNF
as well.  Bits that software has already confirmed in ieee_state belong
to this or an earlier instruction and are never cleared.

The imprecise path passes no summary.  There the trap was taken somewhere
in the trap shadow, so EXC_SUM is not attribution for the instruction
being re-executed -- and only EV6, which traps precisely and so never
takes that path, has fabricated bits to clear.  For the same reason the
clearing is guarded by implver(), matching swcr_update_status().

On an UP1500 (EV68) this takes the glibc math testsuite from 831 failures
to 28, the remainder being unrelated to exception status.

This belongs with the preceding fix to ieee_swcr_to_fpcr(), and should
not be backported without it -- nor it without this.  That fix stops
FPCR_DNOD being set unconditionally, so denormal operand traps start
firing again.  Those traps very often find an exact result, which is
precisely the case where the old code left the FPCR unwritten and the
fabricated bits visible.  Applied alone it would make spurious exception
flags more common, not less.

One case cannot be resolved here: an inexact instruction without the
software completion suffix never traps, so its INE reaches the FPCR
without being recorded anywhere else.  Such a bit is indistinguishable
from an INE the hardware fabricated for a trapping instruction, and is
lost if an underflow or overflow trap with an exact result follows it.
The FPCR is the only record of those instructions and it carries no
attribution.

The bug predates the git history, so there is no commit to reference in a
Fixes tag.

Cc: stable@vger.kernel.org # 5.15+
Signed-off-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Magnus Lindholm <linmag7@gmail.com>
Tested-by: Magnus Lindholm <linmag7@gmail.com>
Link: https://lore.kernel.org/r/20260803-alpha-fp-exceptions-v1-2-c99d75608e60@gmail.com
Signed-off-by: Magnus Lindholm <linmag7@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-09-14 13:20:03 +02:00
arch alpha: don't leak hardware-fabricated FP exception bits to user space 2026-09-14 13:20:03 +02:00
block partitions: aix: bound the pp_count scan to the ppe array 2026-07-24 15:51:24 +02:00
certs X.509: Fix validation of ASN.1 certificate header 2026-07-24 15:51:59 +02:00
crypto crypto: ccm - Set rfc4309 maxauthsize from child 2026-08-23 14:17:31 +02:00
Documentation mm/swap: reject swapon() on filesystem-level encrypted files 2026-09-02 14:27:28 +02:00
drivers usb: usbfs: fix use-after-free of usb_device in usbdev_release() 2026-09-02 14:27:29 +02:00
fs fuse: fix invalidate lock leak on open O_TRUNC DAX failure 2026-09-02 14:27:28 +02:00
include usb: gadget: f_tcm: keep port count until LUN teardown completes 2026-09-02 14:27:28 +02:00
init bootconfig: move xbc_snprint_cmdline() to lib/bootconfig.c 2026-08-23 14:17:24 +02:00
io_uring io_uring/io-wq: fix worker accounting when canceling creation callbacks 2026-09-02 14:27:25 +02:00
ipc ipc/shm: serialize orphan cleanup with shm_nattch updates 2026-06-19 13:33:38 +02:00
kernel kcov: fix data corruption and race conditions on PREEMPT_RT 2026-09-02 14:27:27 +02:00
lib kcov: fix data corruption and race conditions on PREEMPT_RT 2026-09-02 14:27:27 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/swap: reject swapon() on filesystem-level encrypted files 2026-09-02 14:27:28 +02:00
net ipv6: seg6: clear IPv4 control block on IPIP decapsulation 2026-09-02 14:27:28 +02:00
samples tracing/events: Fix to check the simple_tsk_fn creation 2026-07-24 15:51:42 +02:00
scripts kconfig: fix potential NULL pointer dereference in conf_askvalue 2026-07-24 15:51:28 +02:00
security selinux: switch two allocations to use kzalloc_objs() 2026-09-02 14:27:26 +02:00
sound ALSA: aloop: Fix racy access at PCM trigger 2026-09-14 13:20:03 +02:00
tools selftests/ftrace: refactor eprobes test to fix argument checks 2026-08-19 17:14:13 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-06-27 11:05:22 +01:00
virt KVM: Rename mmu_notifier_* to mmu_invalidate_* 2026-08-27 14:28:21 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:11:10 +02:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS staging: rtl8712: Remove driver using deprecated API wext 2025-12-07 06:09:36 +09:00
Makefile Linux 5.15.220 2026-09-02 14:27:29 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.