[PATCH AUTOSEL 6.12 18/21] riscv: vdso: Exclude .rodata from the PT_DYNAMIC segment

[Sasha Levin <sashal@kernel.org>]

From: Fangrui Song <i@maskray.me>

[ Upstream commit e0eb1b6b0cd29ca7793c501d5960fd36ba11f110 ]

.rodata is implicitly included in the PT_DYNAMIC segment due to
inheriting the segment of the preceding .dynamic section (in both GNU ld
and LLD).  When the .rodata section's size is not a multiple of 16
bytes on riscv64, llvm-readelf will report a "PT_DYNAMIC dynamic table
is invalid" warning.  Note: in the presence of the .dynamic section, GNU
readelf and llvm-readelf's -d option decodes the dynamic section using
the section.

This issue arose after commit 8f8c1ff879fab60f80f3a7aec3000f47e5b03ba9
("riscv: vdso.lds.S: remove hardcoded 0x800 .text start addr"), which
placed .rodata directly after .dynamic by removing .eh_frame.

This patch resolves the implicit inclusion into PT_DYNAMIC by explicitly
specifying the :text output section phdr.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://github.com/ClangBuiltLinux/linux/issues/2093
Signed-off-by: Fangrui Song <i@maskray.me>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20250602-riscv-vdso-v1-1-0620cf63cff0@maskray.me
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

**YES**

This commit should be backported to stable kernel trees for the
following reasons:

1. **Regression Fix**: The commit explicitly fixes a regression
   introduced by commit 8f8c1ff879fab60f80f3a7aec3000f47e5b03ba9
   ("riscv: vdso.lds.S: remove hardcoded 0x800 .text start addr").
   Regression fixes are high-priority candidates for stable backporting.

2. **Fixes Invalid ELF Structure**: The issue is not merely cosmetic.
   The PT_DYNAMIC segment is reported as "invalid" by llvm-readelf,
   indicating the ELF structure is technically incorrect. From the
   linker script:
  ```
  .dynamic        : { *(.dynamic) }               :text   :dynamic
  .rodata         : {
  ...
  }  // implicitly inherits :dynamic from previous section
  ```
  Without the explicit `:text` specification, `.rodata` inherits the
  segment attributes from the preceding `.dynamic` section, incorrectly
  including it in the PT_DYNAMIC segment.

3. **Minimal and Safe Change**: The fix is a single-line change that
   adds `:text` to the `.rodata` section definition:
  ```diff
   - }
   +    }                                               :text
   ```
   This explicitly places `.rodata` in the text segment only, excluding
it from PT_DYNAMIC. The change has no functional impact beyond
correcting the ELF structure.

4. **Similar to Previous Backported Commits**: This is similar to commit
   #2 in the reference list ("riscv: vdso: fix section overlapping under
   some conditions") which was marked YES for backporting. Both commits
   fix structural issues in the vDSO linker script that cause
   build/tooling errors.

5. **Potential for Broader Impact**: While the immediate symptom is a
   warning from llvm-readelf, an invalid PT_DYNAMIC segment could
   potentially cause issues with:
   - Build systems that validate ELF structures
   - Runtime loaders with strict ELF validation
   - Debugging and analysis tools
   - Future toolchain versions that may be less tolerant of invalid
     structures

The commit meets the stable tree criteria: it fixes an important bug
(invalid ELF structure), the fix is small and contained, and there's
minimal risk of regression.

 arch/riscv/kernel/vdso/vdso.lds.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/vdso/vdso.lds.S b/arch/riscv/kernel/vdso/vdso.lds.S
index cbe2a179331d2..99e51f7755393 100644
--- a/arch/riscv/kernel/vdso/vdso.lds.S
+++ b/arch/riscv/kernel/vdso/vdso.lds.S
@@ -31,7 +31,7 @@ SECTIONS
 		*(.data .data.* .gnu.linkonce.d.*)
 		*(.dynbss)
 		*(.bss .bss.* .gnu.linkonce.b.*)
-	}
+	}						:text
 
 	.note		: { *(.note.*) }		:text	:note
 
-- 
2.39.5