+ riscv-avoid-fortify-warning-in-syscall_get_arguments.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: riscv: avoid fortify warning in syscall_get_arguments()
has been added to the -mm mm-new branch.  Its filename is
     riscv-avoid-fortify-warning-in-syscall_get_arguments.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/riscv-avoid-fortify-warning-in-syscall_get_arguments.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Nathan Chancellor <nathan@kernel.org>
Subject: riscv: avoid fortify warning in syscall_get_arguments()
Date: Wed, 09 Apr 2025 14:24:46 -0700

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.

Link: https://lkml.kernel.org/r/20250409-riscv-avoid-fortify-warning-syscall_get_arguments-v1-1-7853436d4755@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Dmitry V. Levin <ldv@strace.io>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Charlie Jenkins <charlie@rivosinc.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/riscv/include/asm/syscall.h |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/arch/riscv/include/asm/syscall.h~riscv-avoid-fortify-warning-in-syscall_get_arguments
+++ a/arch/riscv/include/asm/syscall.h
@@ -62,8 +62,11 @@ static inline void syscall_get_arguments
 					 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,
_

Patches currently in -mm which might be from nathan@kernel.org are

riscv-avoid-fortify-warning-in-syscall_get_arguments.patch