[PATCH AUTOSEL 6.11 110/244] x86/syscall: Avoid memcpy() for ia32 syscall_get_arguments()

Sasha Levin
2024-09-25T11:41:55Z

From: Kees Cook <kees@kernel.org>

[ Upstream commit d19d638b1e6cf746263ef60b7d0dee0204d8216a ]

Modern (fortified) memcpy() prefers to avoid writing (or reading) beyond
the end of the addressed destination (or source) struct member:

In function ‘fortify_memcpy_chk’,
inlined from ‘syscall_get_arguments’ at ./arch/x86/include/asm/syscall.h:85:2,
inlined from ‘populate_seccomp_data’ at kernel/seccomp.c:258:2,
inlined from ‘__seccomp_filter’ at kernel/seccomp.c:1231:3:
./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);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As already done for x86_64 and compat mode, do not use memcpy() to
extract syscall arguments from struct pt_regs but rather just perform
direct assignments. Binary output differences are negligible, and actually
ends up using less stack space:

- sub $0x84,%esp
+ sub $0x6c,%esp

and less text size:

text data bss dec hex filename
10794 252 0 11046 2b26 gcc-32b/kernel/seccomp.o.stock
10714 252 0 10966 2ad6 gcc-32b/kernel/seccomp.o.after

Closes: https://lore.kernel.org/lkml/9b69fb14-df89-4677-9c82-056ea9e706f5@gmail.com/
Reported-by: Mirsad Todorovac <mtodorovac69@gmail.com>
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Mirsad Todorovac <mtodorovac69@gmail.com>
Link: https://lore.kernel.org/all/20240708202202.work.477-kees%40kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/include/asm/syscall.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
index 2fc7bc3863ff6..7c488ff0c7641 100644
--- a/arch/x86/include/asm/syscall.h
+++ b/arch/x86/include/asm/syscall.h
@@ -82,7 +82,12 @@ static inline void syscall_get_arguments(struct task_struct *task,
struct pt_regs *regs,
unsigned long *args)
{
- memcpy(args, &regs->bx, 6 * sizeof(args[0]));
+ args[0] = regs->bx;
+ args[1] = regs->cx;
+ args[2] = regs->dx;
+ args[3] = regs->si;
+ args[4] = regs->di;
+ args[5] = regs->bp;
}

static inline int syscall_get_arch(struct task_struct *task)
--
2.43.0