linux-kernel - [PATCH bpf-next v3 2/3] bpf, x86: clean garbage value in the stack of trampoline

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Message-Id: <20230607125911.145345-3-imagedong@tencent.com>
Date:   Wed,  7 Jun 2023 20:59:10 +0800
From:   menglong8.dong@...il.com
To:     alexei.starovoitov@...il.com
Cc:     davem@...emloft.net, dsahern@...nel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev,
        song@...nel.org, yhs@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, sdf@...gle.com, x86@...nel.org,
        imagedong@...cent.com, benbjiang@...cent.com,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next v3 2/3] bpf, x86: clean garbage value in the stack of trampoline

From: Menglong Dong <imagedong@...cent.com>

There are garbage values in upper bytes when we store the arguments
into stack in save_regs() if the size of the argument less then 8.

As we already reserve 8 byte for the arguments in regs and stack,
it is ok to store/restore the regs in BPF_DW size. Then, the garbage
values in upper bytes will be cleaned.

Reviewed-by: Jiang Biao <benbjiang@...cent.com>
Signed-off-by: Menglong Dong <imagedong@...cent.com>
---
 arch/x86/net/bpf_jit_comp.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 413b986b5afd..e9bc0b50656b 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1878,20 +1878,16 @@ static void save_regs(const struct btf_func_model *m, u8 **prog, int nr_regs,
 
 		if (i <= 5) {
 			/* copy function arguments from regs into stack */
-			emit_stx(prog, bytes_to_bpf_size(arg_size),
-				 BPF_REG_FP,
+			emit_stx(prog, BPF_DW, BPF_REG_FP,
 				 i == 5 ? X86_REG_R9 : BPF_REG_1 + i,
 				 -(stack_size - i * 8));
 		} else {
 			/* copy function arguments from origin stack frame
 			 * into current stack frame.
 			 */
-			emit_ldx(prog, bytes_to_bpf_size(arg_size),
-				 BPF_REG_0, BPF_REG_FP,
+			emit_ldx(prog, BPF_DW, BPF_REG_0, BPF_REG_FP,
 				 (i - 6) * 8 + 0x18);
-			emit_stx(prog, bytes_to_bpf_size(arg_size),
-				 BPF_REG_FP,
-				 BPF_REG_0,
+			emit_stx(prog, BPF_DW, BPF_REG_FP, BPF_REG_0,
 				 -(stack_size - i * 8));
 		}
 
@@ -1918,7 +1914,7 @@ static void restore_regs(const struct btf_func_model *m, u8 **prog, int nr_regs,
 			next_same_struct = !next_same_struct;
 		}
 
-		emit_ldx(prog, bytes_to_bpf_size(arg_size),
+		emit_ldx(prog, BPF_DW,
 			 i == 5 ? X86_REG_R9 : BPF_REG_1 + i,
 			 BPF_REG_FP,
 			 -(stack_size - i * 8));
@@ -1949,12 +1945,9 @@ static void prepare_origin_stack(const struct btf_func_model *m, u8 **prog,
 		}
 
 		if (i > 5) {
-			emit_ldx(prog, bytes_to_bpf_size(arg_size),
-				 BPF_REG_0, BPF_REG_FP,
+			emit_ldx(prog, BPF_DW, BPF_REG_0, BPF_REG_FP,
 				 (i - 6) * 8 + 0x18);
-			emit_stx(prog, bytes_to_bpf_size(arg_size),
-				 BPF_REG_FP,
-				 BPF_REG_0,
+			emit_stx(prog, BPF_DW, BPF_REG_FP, BPF_REG_0,
 				 -(stack_size - (i - 6) * 8));
 		}
 
-- 
2.40.1