vmcoreinfo: include kallsyms symbols

The internal kallsyms tables contain information which could be quite
useful to a debugging tool in the absence of other debuginfo.  If kallsyms
is enabled, then a debugging tool could parse it and use it as a fallback
symbol table.  Combined with BTF data, live & post-mortem debuggers can
support basic operations without needing a large DWARF debuginfo file
available.  As many as five symbols are necessary to properly parse
kallsyms names and addresses.  Add these to the vmcoreinfo note.

CONFIG_KALLSYMS_ABSOLUTE_PERCPU does impact the computation of symbol
addresses.  However, a debugger can infer this configuration value by
comparing the address of _stext in the vmcoreinfo with the address
computed via kallsyms.  So there's no need to include information about
this config value in the vmcoreinfo note.

To verify that we're still well below the maximum of 4096 bytes, I created
a script[1] to compute a rough upper bound on the possible size of
vmcoreinfo.  On v5.18-rc7, the script reports 3106 bytes, and with this
patch, the maximum become 3370 bytes.

[1]: https://github.com/brenns10/kernel_stuff/blob/master/vmcoreinfosize/

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Stephen Brennan <[email protected]>
Acked-by: Baoquan He <[email protected]>
Cc: Bixuan Cui <[email protected]>
Cc: Dave Young <[email protected]>
Cc: David Vernet <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Sami Tolvanen <[email protected]>
Cc: Stephen Boyd <[email protected]>
Cc: Vivek Goyal <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: brenns10

kernel/crash_core.c

@@ -15,6 +15,8 @@
 
 #include <crypto/sha1.h>
 
+#include "kallsyms_internal.h"
+
 /* vmcoreinfo stuff */
 unsigned char *vmcoreinfo_data;
 size_t vmcoreinfo_size;
@@ -480,6 +482,18 @@ static int __init crash_save_vmcoreinfo_init(void)
 	VMCOREINFO_NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE);
 #endif
 
+#ifdef CONFIG_KALLSYMS
+	VMCOREINFO_SYMBOL(kallsyms_names);
+	VMCOREINFO_SYMBOL(kallsyms_token_table);
+	VMCOREINFO_SYMBOL(kallsyms_token_index);
+#ifdef CONFIG_KALLSYMS_BASE_RELATIVE
+	VMCOREINFO_SYMBOL(kallsyms_offsets);
+	VMCOREINFO_SYMBOL(kallsyms_relative_base);
+#else
+	VMCOREINFO_SYMBOL(kallsyms_addresses);
+#endif /* CONFIG_KALLSYMS_BASE_RELATIVE */
+#endif /* CONFIG_KALLSYMS */
+
 	arch_crash_save_vmcoreinfo();
 	update_vmcoreinfo_note();