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From e90c0011d6e9476104c4c43aa76d2d0830a15946 Mon Sep 17 00:00:00 2001
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From: Philipp Rudo <prudo@redhat.com>
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Date: Tue, 9 Nov 2021 14:52:22 +0100
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Subject: [PATCH] Fix live debugging with lockdown=integrity
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With kernel lockdown the access to kernel interfaces that allow to
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extract confidential information (lockdown=confidentiality) or modify a
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running kernel (lockdown=integrity) can be restricted. Two of the
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interfaces that can be restricted are /dev/mem (integrity &
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confidentiality) and /proc/kcore (confidentiality). With
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lockdown=integrity this leads to a situation where /dev/mem exists but
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is not readable while /proc/kcore exists and is readable. This breaks
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crash's live debugging when it is invoked without argument, i.e.
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$ crash
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[...]
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crash: /dev/mem: Operation not permitted
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while passing /proc/kcore as image succeeds. The reason for this is that
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crash always picks /dev/mem as source when it exits but doesn't check if
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it is readable. Fix this by only selecting /dev/mem when it is readable.
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Signed-off-by: Philipp Rudo <prudo@redhat.com>
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---
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filesys.c | 2 +-
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main.c | 2 +-
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2 files changed, 2 insertions(+), 2 deletions(-)
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diff --git a/filesys.c b/filesys.c
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index 3361b6c12ed3..43cbe826fc79 100644
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--- a/filesys.c
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+++ b/filesys.c
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@@ -3666,7 +3666,7 @@ get_live_memory_source(void)
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if (pc->live_memsrc)
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goto live_report;
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- if (file_exists("/dev/mem", NULL))
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+ if (file_readable("/dev/mem"))
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pc->live_memsrc = "/dev/mem";
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else if (file_exists("/proc/kcore", NULL)) {
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pc->flags &= ~DEVMEM;
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diff --git a/main.c b/main.c
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index 388ac46c3834..dfd343cd9dd4 100644
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--- a/main.c
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+++ b/main.c
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@@ -1119,7 +1119,7 @@ setup_environment(int argc, char **argv)
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pc->flags2 |= REDZONE;
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pc->confd = -2;
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pc->machine_type = MACHINE_TYPE;
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- if (file_exists("/dev/mem", NULL)) { /* defaults until argv[] is parsed */
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+ if (file_readable("/dev/mem")) { /* defaults until argv[] is parsed */
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pc->readmem = read_dev_mem;
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pc->writemem = write_dev_mem;
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} else if (file_exists("/proc/kcore", NULL)) {
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--
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2.30.2
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