Patch "perf/callchain: Force USER_DS when invoking perf_callchain_user()" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    perf/callchain: Force USER_DS when invoking perf_callchain_user()

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     perf-callchain-force-user_ds-when-invoking-perf_callchain_user.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Mon Apr  9 17:09:24 CEST 2018
From: Will Deacon <will.deacon@arm.com>
Date: Tue, 9 May 2017 18:00:04 +0100
Subject: perf/callchain: Force USER_DS when invoking perf_callchain_user()

From: Will Deacon <will.deacon@arm.com>


[ Upstream commit 88b0193d9418c00340e45e0a913a0813bc6c8c96 ]

Perf can generate and record a user callchain in response to a synchronous
request, such as a tracepoint firing. If this happens under set_fs(KERNEL_DS),
then we can end up walking the user stack (and dereferencing/saving whatever we
find there) without the protections usually afforded by checks such as
access_ok.

Rather than play whack-a-mole with each architecture's stack unwinding
implementation, fix the root of the problem by ensuring that we force USER_DS
when invoking perf_callchain_user from the perf core.

Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/events/callchain.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -227,12 +227,18 @@ get_perf_callchain(struct pt_regs *regs,
 		}
 
 		if (regs) {
+			mm_segment_t fs;
+
 			if (crosstask)
 				goto exit_put;
 
 			if (add_mark)
 				perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
+
+			fs = get_fs();
+			set_fs(USER_DS);
 			perf_callchain_user(&ctx, regs);
+			set_fs(fs);
 		}
 	}
 


Patches currently in stable-queue which might be from will.deacon@arm.com are

queue-4.9/perf-callchain-force-user_ds-when-invoking-perf_callchain_user.patch
queue-4.9/arm64-pci-fix-struct-acpi_pci_root_ops-allocation-failure-path.patch
queue-4.9/arm64-perf-ignore-exclude_hv-when-kernel-is-running-in-hyp.patch
queue-4.9/arm64-kernel-restrict-dev-mem-read-calls-to-linear-region.patch
queue-4.9/arm64-futex-fix-undefined-behaviour-with-futex_op_oparg_shift-usage.patch