The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 5ae5fbd2107959b68ac69a8b75412208663aea88 Mon Sep 17 00:00:00 2001
From: Athira Rajeev atrajeev@linux.vnet.ibm.com Date: Thu, 25 Feb 2021 05:10:39 -0500 Subject: [PATCH] powerpc/perf: Fix handling of privilege level checks in perf interrupt context
Running "perf mem record" in powerpc platforms with selinux enabled resulted in soft lockup's. Below call-trace was seen in the logs:
CPU: 58 PID: 3751 Comm: sssd_nss Not tainted 5.11.0-rc7+ #2 NIP: c000000000dff3d4 LR: c000000000dff3d0 CTR: 0000000000000000 REGS: c000007fffab7d60 TRAP: 0100 Not tainted (5.11.0-rc7+) ... NIP _raw_spin_lock_irqsave+0x94/0x120 LR _raw_spin_lock_irqsave+0x90/0x120 Call Trace: 0xc00000000fd47260 (unreliable) skb_queue_tail+0x3c/0x90 audit_log_end+0x6c/0x180 common_lsm_audit+0xb0/0xe0 slow_avc_audit+0xa4/0x110 avc_has_perm+0x1c4/0x260 selinux_perf_event_open+0x74/0xd0 security_perf_event_open+0x68/0xc0 record_and_restart+0x6e8/0x7f0 perf_event_interrupt+0x22c/0x560 performance_monitor_exception0x4c/0x60 performance_monitor_common_virt+0x1c8/0x1d0 interrupt: f00 at _raw_spin_lock_irqsave+0x38/0x120 NIP: c000000000dff378 LR: c000000000b5fbbc CTR: c0000000007d47f0 REGS: c00000000fd47860 TRAP: 0f00 Not tainted (5.11.0-rc7+) ... NIP _raw_spin_lock_irqsave+0x38/0x120 LR skb_queue_tail+0x3c/0x90 interrupt: f00 0x38 (unreliable) 0xc00000000aae6200 audit_log_end+0x6c/0x180 audit_log_exit+0x344/0xf80 __audit_syscall_exit+0x2c0/0x320 do_syscall_trace_leave+0x148/0x200 syscall_exit_prepare+0x324/0x390 system_call_common+0xfc/0x27c
The above trace shows that while the CPU was handling a performance monitor exception, there was a call to security_perf_event_open() function. In powerpc core-book3s, this function is called from perf_allow_kernel() check during recording of data address in the sample via perf_get_data_addr().
Commit da97e18458fb ("perf_event: Add support for LSM and SELinux checks") introduced security enhancements to perf. As part of this commit, the new security hook for perf_event_open() was added in all places where perf paranoid check was previously used. In powerpc core-book3s code, originally had paranoid checks in perf_get_data_addr() and power_pmu_bhrb_read(). So perf_paranoid_kernel() checks were replaced with perf_allow_kernel() in these PMU helper functions as well.
The intention of paranoid checks in core-book3s was to verify privilege access before capturing some of the sample data. Along with paranoid checks, perf_allow_kernel() also does a security_perf_event_open(). Since these functions are accessed while recording a sample, we end up calling selinux_perf_event_open() in PMI context. Some of the security functions use spinlock like sidtab_sid2str_put(). If a perf interrupt hits under a spin lock and if we end up in calling selinux hook functions in PMI handler, this could cause a dead lock.
Since the purpose of this security hook is to control access to perf_event_open(), it is not right to call this in interrupt context.
The paranoid checks in powerpc core-book3s were done at interrupt time which is also not correct.
Reference commits: Commit cd1231d7035f ("powerpc/perf: Prevent kernel address leak via perf_get_data_addr()") Commit bb19af816025 ("powerpc/perf: Prevent kernel address leak to userspace via BHRB buffer")
We only allow creation of events that have already passed the privilege checks in perf_event_open(). So these paranoid checks are not needed at event time. As a fix, patch uses 'event->attr.exclude_kernel' check to prevent exposing kernel address for userspace only sampling.
Fixes: cd1231d7035f ("powerpc/perf: Prevent kernel address leak via perf_get_data_addr()") Cc: stable@vger.kernel.org # v4.17+ Suggested-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Athira Rajeev atrajeev@linux.vnet.ibm.com Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/1614247839-1428-1-git-send-email-atrajeev@linux.vn...
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c index 6817331e22ff..766f064f00fb 100644 --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -222,7 +222,7 @@ static inline void perf_get_data_addr(struct perf_event *event, struct pt_regs * if (!(mmcra & MMCRA_SAMPLE_ENABLE) || sdar_valid) *addrp = mfspr(SPRN_SDAR);
- if (is_kernel_addr(mfspr(SPRN_SDAR)) && perf_allow_kernel(&event->attr) != 0) + if (is_kernel_addr(mfspr(SPRN_SDAR)) && event->attr.exclude_kernel) *addrp = 0; }
@@ -507,7 +507,7 @@ static void power_pmu_bhrb_read(struct perf_event *event, struct cpu_hw_events * * addresses, hence include a check before filtering code */ if (!(ppmu->flags & PPMU_ARCH_31) && - is_kernel_addr(addr) && perf_allow_kernel(&event->attr) != 0) + is_kernel_addr(addr) && event->attr.exclude_kernel) continue;
/* Branches are read most recent first (ie. mfbhrb 0 is