RISC-V NOMMU flat binaries cannot tolerate a gap between the text and
data section as the toolchain fully resolve at compile time the PC
relative global pointer (__global_pointer$ value loaded in gp register).
Without a relocation entry provided, the flat bin loader cannot fix the
value if a gap is introduced and executables fail to run.
This series fixes this problem by allowing an architecture to request
the flat loader to suppress the gap between the text and data sections.
The first patch fixes binfmt_flat flat_load_file(). The second patch
adds the asm/flat.h file to riscv arch to request the gap suppression
using the newly introduced macro FLAT_TEXT_DATA_NO_GAP.
These patches do not change the binfmt_flat loader behavior for other
architectures.
Damien Le Moal (2):
binfmt_flat: allow not offsetting data start
riscv: introduce asm/flat.h
arch/riscv/include/asm/Kbuild | 1 -
arch/riscv/include/asm/flat.h | 29 +++++++++++++++++++++++++++++
fs/binfmt_flat.c | 25 +++++++++++++++++++------
3 files changed, 48 insertions(+), 7 deletions(-)
create mode 100644 arch/riscv/include/asm/flat.h
--
2.30.2
uclibc/gcc combined with elf2flt riscv linker file fully resolve the
PC relative __global_pointer$ value at compile time and do not generate
a relocation entry to set a runtime gp value. As a result, if the
flatbin loader introduces a gap between the text and data sections, the
gp value becomes incorrect and prevent correct execution of a flatbin
executable. Avoid this problem by introducing the file asm/flat.h
and defining the macro FLAT_TEXT_DATA_NO_GAP to indicate that the text
and data sections must be loaded at contiguous addresses.
Signed-off-by: Damien Le Moal <[email protected]>
---
arch/riscv/include/asm/Kbuild | 1 -
arch/riscv/include/asm/flat.h | 29 +++++++++++++++++++++++++++++
2 files changed, 29 insertions(+), 1 deletion(-)
create mode 100644 arch/riscv/include/asm/flat.h
diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
index 445ccc97305a..a8b54a3f4c2b 100644
--- a/arch/riscv/include/asm/Kbuild
+++ b/arch/riscv/include/asm/Kbuild
@@ -1,7 +1,6 @@
# SPDX-License-Identifier: GPL-2.0
generic-y += early_ioremap.h
generic-y += extable.h
-generic-y += flat.h
generic-y += kvm_para.h
generic-y += user.h
generic-y += vmlinux.lds.h
diff --git a/arch/riscv/include/asm/flat.h b/arch/riscv/include/asm/flat.h
new file mode 100644
index 000000000000..43bccf090fd1
--- /dev/null
+++ b/arch/riscv/include/asm/flat.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RISCV_FLAT_H
+#define _ASM_RISCV_FLAT_H
+
+#include <asm/unaligned.h>
+
+static inline int flat_get_addr_from_rp(u32 __user *rp, u32 relval, u32 flags,
+ u32 *addr)
+{
+ *addr = get_unaligned((__force u32 *)rp);
+ return 0;
+}
+
+static inline int flat_put_addr_at_rp(u32 __user *rp, u32 addr, u32 rel)
+{
+ put_unaligned(addr, (__force u32 *)rp);
+ return 0;
+}
+
+/*
+ * uclibc/gcc fully resolve the PC relative __global_pointer value
+ * at compile time and do not generate a relocation entry to set a
+ * runtime gp value. As a result, the flatbin loader must not introduce
+ * a gap between the text and data sections and keep them contiguous to
+ * avoid invalid address accesses.
+ */
+#define FLAT_TEXT_DATA_NO_GAP (1)
+
+#endif /* _ASM_RISCV_FLAT_H */
--
2.30.2