[PATCH AUTOSEL 5.4 3/3] riscv: Avoid fortify warning in syscall_get_arguments()

[Sasha Levin <sashal@kernel.org>]

From: Nathan Chancellor <nathan@kernel.org>

[ Upstream commit 1413708f990cb7d025affd706ba9c23e2bfc1a27 ]

When building with CONFIG_FORTIFY_SOURCE=y and W=1, there is a warning
because of the memcpy() in syscall_get_arguments():

  In file included from include/linux/string.h:392,
                   from include/linux/bitmap.h:13,
                   from include/linux/cpumask.h:12,
                   from arch/riscv/include/asm/processor.h:55,
                   from include/linux/sched.h:13,
                   from kernel/ptrace.c:13:
  In function 'fortify_memcpy_chk',
      inlined from 'syscall_get_arguments.isra' at arch/riscv/include/asm/syscall.h:66:2:
  include/linux/fortify-string.h:580:25: error: call to '__read_overflow2_field' declared with attribute warning: detected read beyond size of field (2nd parameter); maybe use struct_group()? [-Werror=attribute-warning]
    580 |                         __read_overflow2_field(q_size_field, size);
        |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

The fortified memcpy() routine enforces that the source is not overread
and the destination is not overwritten if the size of either field and
the size of the copy are known at compile time. The memcpy() in
syscall_get_arguments() intentionally overreads from a1 to a5 in
'struct pt_regs' but this is bigger than the size of a1.

Normally, this could be solved by wrapping a1 through a5 with
struct_group() but there was already a struct_group() applied to these
members in commit bba547810c66 ("riscv: tracing: Fix
__write_overflow_field in ftrace_partial_regs()").

Just avoid memcpy() altogether and write the copying of args from regs
manually, which clears up the warning at the expense of three extra
lines of code.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Dmitry V. Levin <ldv@strace.io>
Link: https://lore.kernel.org/r/20250409-riscv-avoid-fortify-warning-syscall_get_arguments-v1-1-7853436d4755@kernel.org
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/riscv/include/asm/syscall.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
index 42347d0981e7e..e53690b30bbeb 100644
--- a/arch/riscv/include/asm/syscall.h
+++ b/arch/riscv/include/asm/syscall.h
@@ -67,8 +67,11 @@ static inline void syscall_get_arguments(struct task_struct *task,
 					 unsigned long *args)
 {
 	args[0] = regs->orig_a0;
-	args++;
-	memcpy(args, &regs->a1, 5 * sizeof(args[0]));
+	args[1] = regs->a1;
+	args[2] = regs->a2;
+	args[3] = regs->a3;
+	args[4] = regs->a4;
+	args[5] = regs->a5;
 }
 
 static inline void syscall_set_arguments(struct task_struct *task,
-- 
2.39.5


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