arch: fix broken BuildID for arm64 and riscv

commit fe15ce495a511c71ffb78121ce0b6d8ca33dc5fd upstream.

Dennis Gilmore reports that the BuildID is missing in the arm64 vmlinux
since commit 47547576d4c3 ("arm64: remove special treatment for the
link order of head.o").

The issue is that the type of .notes section, which contains the BuildID,
changed from NOTES to PROGBITS.

Ard Biesheuvel figured out that whichever object gets linked first gets
to decide the type of a section. The PROGBITS type is the result of the
compiler emitting .note.GNU-stack as PROGBITS rather than NOTE.

While Ard provided a fix for arm64, I want to fix this globally because
the same issue is happening on riscv since commit 72506fddc7f8 ("riscv:
remove special treatment for the link order of head.o"). This problem
will happen in general for other architectures if they start to drop
unneeded entries from scripts/head-object-list.txt.

Discard .note.GNU-stack in include/asm-generic/vmlinux.lds.h.

Link: https://lore.kernel.org/lkml/CAABkxwuQoz1CTbyb57n0ZX65eSYiTonFCU8-LCQc=74D=xE=rA@mail.gmail.com/
Fixes: 47547576d4c3 ("arm64: remove special treatment for the link order of head.o")
Fixes: 72506fddc7f8 ("riscv: remove special treatment for the link order of head.o")
Reported-by: Dennis Gilmore <dennis@ausil.us>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
[Tom: stable backport 5.15.y, 5.10.y, 5.4.y]

Though the above "Fixes:" commits are not in this kernel, the conditions
which lead to a missing Build ID in arm64 vmlinux are similar.

Evidence points to these conditions:
1. ld version > 2.36 (exact binutils commit documented in a494398bde27)
2. first object which gets linked (head.o) has a PROGBITS .note.GNU-stack segment

These conditions can be observed when:
- 5.15.60+ OR 5.10.136+ OR 5.4.210+
- AND ld version > 2.36
- AND arch=arm64
- AND CONFIG_MODVERSIONS=y

There are notable differences in the vmlinux elf files produced
before(bad) and after(good) applying this series.

Good: p_type:PT_NOTE segment exists.
 Bad: p_type:PT_NOTE segment is missing.

Good: sh_name_str:.notes section has sh_type:SHT_NOTE
 Bad: sh_name_str:.notes section has sh_type:SHT_PROGBITS

`readelf -n` (as of v2.40) searches for Build Id
by processing only the very first note in sh_type:SHT_NOTE sections.

This was previously bisected to the stable backport of 1ccae403d960.
Follow-up experiments were discussed here: https://lore.kernel.org/all/20221221235413.xaisboqmr7dkqwn6@oracle.com/
which strongly hints at condition 2.
Signed-off-by: Tom Saeger <tom.saeger@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 2d45d98773e232134dd94099eabce1574b4806f5..a68535f36d13548f057dc2201b7c318ba2397e85 100644 (file)
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -825,7 +825,12 @@
 #define TRACEDATA
 #endif
 
+/*
+ * Discard .note.GNU-stack, which is emitted as PROGBITS by the compiler.
+ * Otherwise, the type of .notes section would become PROGBITS instead of NOTES.
+ */
 #define NOTES                                                          \
+       /DISCARD/ : { *(.note.GNU-stack) }                              \
        .notes : AT(ADDR(.notes) - LOAD_OFFSET) {                       \
                __start_notes = .;                                      \
                KEEP(*(.note.*))                                        \