Marco Elver 60768ffced signal: Deliver SIGTRAP on perf event asynchronously if blocked ... [ Upstream commit 78ed93d72d ] With SIGTRAP on perf events, we have encountered termination of processes due to user space attempting to block delivery of SIGTRAP. Consider this case: <set up SIGTRAP on a perf event> ... sigset_t s; sigemptyset(&s); sigaddset(&s, SIGTRAP | <and others>); sigprocmask(SIG_BLOCK, &s, ...); ... <perf event triggers> When the perf event triggers, while SIGTRAP is blocked, force_sig_perf() will force the signal, but revert back to the default handler, thus terminating the task. This makes sense for error conditions, but not so much for explicitly requested monitoring. However, the expectation is still that signals generated by perf events are synchronous, which will no longer be the case if the signal is blocked and delivered later. To give user space the ability to clearly distinguish synchronous from asynchronous signals, introduce siginfo_t::si_perf_flags and TRAP_PERF_FLAG_ASYNC (opted for flags in case more binary information is required in future). The resolution to the problem is then to (a) no longer force the signal (avoiding the terminations), but (b) tell user space via si_perf_flags if the signal was synchronous or not, so that such signals can be handled differently (e.g. let user space decide to ignore or consider the data imprecise). The alternative of making the kernel ignore SIGTRAP on perf events if the signal is blocked may work for some usecases, but likely causes issues in others that then have to revert back to interception of sigprocmask() (which we want to avoid). [ A concrete example: when using breakpoint perf events to track data-flow, in a region of code where signals are blocked, data-flow can no longer be tracked accurately. When a relevant asynchronous signal is received after unblocking the signal, the data-flow tracking logic needs to know its state is imprecise. ] Fixes: 97ba62b278 ("perf: Add support for SIGTRAP on perf events") Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Tested-by: Dmitry Vyukov <dvyukov@google.com> Link: https://lore.kernel.org/r/20220404111204.935357-1-elver@google.com Signed-off-by: Sasha Levin <sashal@kernel.org>		2022-06-09 10:22:48 +02:00
..
boot	ARM: dts: exynos: add atmel,24c128 fallback to Samsung EEPROM	2022-06-09 10:22:42 +02:00
common
configs	ARM: configs: multi_v5_defconfig: re-enable DRM_PANEL and FB_xxx	2022-04-08 14:23:23 +02:00
crypto	lib/crypto: blake2s: avoid indirect calls to compression function for Clang CFI	2022-05-30 09:28:59 +02:00
include	arm: use fallback for random_get_entropy() instead of zero	2022-05-30 09:29:14 +02:00
kernel	signal: Deliver SIGTRAP on perf event asynchronously if blocked	2022-06-09 10:22:48 +02:00
lib
mach-actions
mach-alpine
mach-artpec
mach-asm9260
mach-aspeed
mach-at91
mach-axxia
mach-bcm
mach-berlin
mach-clps711x
mach-cns3xxx
mach-davinci	ARM: davinci: da850-evm: Avoid NULL pointer dereference	2022-04-20 09:34:20 +02:00
mach-digicolor
mach-dove
mach-ep93xx
mach-exynos	pinctrl: samsung: fix missing GPIOLIB on ARM64 Exynos config	2022-05-09 09:14:30 +02:00
mach-footbridge
mach-gemini
mach-highbank
mach-hisi	ARM: hisi: Add missing of_node_put after of_find_compatible_node	2022-06-09 10:22:42 +02:00
mach-imx	ARM: imx: register reset controller from a platform driver	2021-10-15 09:38:06 +08:00
mach-integrator
mach-iop32x	ARM: iop32x: offset IRQ numbers by 1	2022-04-08 14:24:11 +02:00
mach-ixp4xx
mach-keystone
mach-lpc18xx
mach-lpc32xx
mach-mediatek
mach-meson
mach-milbeaut
mach-mmp	ARM: mmp: Fix failure to remove sram device	2022-04-08 14:24:02 +02:00
mach-moxart
mach-mstar	ARM: mstar: Select HAVE_ARM_ARCH_TIMER	2022-04-08 14:22:46 +02:00
mach-mv78xx0
mach-mvebu
mach-mxs
mach-nomadik
mach-npcm
mach-nspire
mach-omap1	ARM: OMAP1: clock: Fix UART rate reporting algorithm	2022-06-09 10:22:42 +02:00
mach-omap2	ARM: OMAP2+: Fix refcount leak in omap_gic_of_init	2022-05-09 09:14:32 +02:00
mach-orion5x
mach-oxnas
mach-pxa
mach-qcom
mach-rda
mach-realtek
mach-realview
mach-rockchip
mach-rpc
mach-s3c	ARM: 9187/1: JIVE: fix return value of __setup handler	2022-04-08 14:24:13 +02:00
mach-s5pv210
mach-sa1100
mach-shmobile	ARM: shmobile: rcar-gen2: Add missing of_node_put()	2022-01-27 11:04:25 +01:00
mach-socfpga	ARM: socfpga: fix missing RESET_CONTROLLER	2022-02-16 12:56:19 +01:00
mach-spear
mach-sti
mach-stm32
mach-sunxi
mach-tegra
mach-uniphier
mach-ux500
mach-versatile
mach-vexpress	ARM: versatile: Add missing of_node_put in dcscb_init	2022-06-09 10:22:42 +02:00
mach-vt8500
mach-zynq
mm	ARM: 9196/1: spectre-bhb: enable for Cortex-A15	2022-05-25 09:57:33 +02:00
net
nwfpe
plat-omap
plat-orion
plat-pxa
plat-versatile
probes	ARM: 9170/1: fix panic when kasan and kprobe are enabled	2022-02-01 17:27:07 +01:00
tools
vdso
vfp
xen
Kbuild
Kconfig	kmap_local: don't assume kmap PTEs are linear arrays in memory	2021-11-25 09:48:43 +01:00
Kconfig-nommu
Kconfig.assembler
Kconfig.debug	ARM: imx: rename DEBUG_IMX21_IMX27_UART to DEBUG_IMX27_UART	2022-01-27 11:04:29 +01:00
Makefile	ARM: 9156/1: drop cc-option fallbacks for architecture selection	2021-11-18 19:17:13 +01:00