netdev - [PATCH bpf 2/3] bpf, x32: Fix bug with ALU64 {LSH,RSH,ARSH} BPF

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Date:   Fri, 28 Jun 2019 22:57:50 -0700
From:   Luke Nelson <lukenels@...washington.edu>
To:     linux-kernel@...r.kernel.org
Cc:     Luke Nelson <luke.r.nels@...il.com>, Xi Wang <xi.wang@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Wang YanQing <udknight@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Shuah Khan <shuah@...nel.org>,
        Jiong Wang <jiong.wang@...ronome.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Björn Töpel <bjorn.topel@...il.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: [PATCH bpf 2/3] bpf, x32: Fix bug with ALU64 {LSH,RSH,ARSH} BPF_K shift by 0

The current x32 BPF JIT does not correctly compile shift operations when
the immediate shift amount is 0. The expected behavior is for this to
be a no-op.

The following program demonstrates the bug. The expexceted result is 1,
but the current JITed code returns 2.

  r0 = 1
  r1 = 1
  r1 <<= 0
  if r1 == 1 goto end
  r0 = 2
end:
  exit

This patch simplifies the code and fixes the bug.

Fixes: 03f5781be2c7 ("bpf, x86_32: add eBPF JIT compiler for ia32")
Co-developed-by: Xi Wang <xi.wang@...il.com>
Signed-off-by: Xi Wang <xi.wang@...il.com>
Signed-off-by: Luke Nelson <luke.r.nels@...il.com>
---
 arch/x86/net/bpf_jit_comp32.c | 63 ++++-------------------------------
 1 file changed, 6 insertions(+), 57 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c
index f34ef513f4f9..1d12d2174085 100644
--- a/arch/x86/net/bpf_jit_comp32.c
+++ b/arch/x86/net/bpf_jit_comp32.c
@@ -894,27 +894,10 @@ static inline void emit_ia32_lsh_i64(const u8 dst[], const u32 val,
 	}
 	/* Do LSH operation */
 	if (val < 32) {
-		/* shl dreg_hi,imm8 */
-		EMIT3(0xC1, add_1reg(0xE0, dreg_hi), val);
-		/* mov ebx,dreg_lo */
-		EMIT2(0x8B, add_2reg(0xC0, dreg_lo, IA32_EBX));
+		/* shld dreg_hi,dreg_lo,imm8 */
+		EMIT4(0x0F, 0xA4, add_2reg(0xC0, dreg_hi, dreg_lo), val);
 		/* shl dreg_lo,imm8 */
 		EMIT3(0xC1, add_1reg(0xE0, dreg_lo), val);
-
-		/* IA32_ECX = 32 - val */
-		/* mov ecx,val */
-		EMIT2(0xB1, val);
-		/* movzx ecx,ecx */
-		EMIT3(0x0F, 0xB6, add_2reg(0xC0, IA32_ECX, IA32_ECX));
-		/* neg ecx */
-		EMIT2(0xF7, add_1reg(0xD8, IA32_ECX));
-		/* add ecx,32 */
-		EMIT3(0x83, add_1reg(0xC0, IA32_ECX), 32);
-
-		/* shr ebx,cl */
-		EMIT2(0xD3, add_1reg(0xE8, IA32_EBX));
-		/* or dreg_hi,ebx */
-		EMIT2(0x09, add_2reg(0xC0, dreg_hi, IA32_EBX));
 	} else if (val >= 32 && val < 64) {
 		u32 value = val - 32;
 
@@ -960,27 +943,10 @@ static inline void emit_ia32_rsh_i64(const u8 dst[], const u32 val,
 
 	/* Do RSH operation */
 	if (val < 32) {
-		/* shr dreg_lo,imm8 */
-		EMIT3(0xC1, add_1reg(0xE8, dreg_lo), val);
-		/* mov ebx,dreg_hi */
-		EMIT2(0x8B, add_2reg(0xC0, dreg_hi, IA32_EBX));
+		/* shrd dreg_lo,dreg_hi,imm8 */
+		EMIT4(0x0F, 0xAC, add_2reg(0xC0, dreg_lo, dreg_hi), val);
 		/* shr dreg_hi,imm8 */
 		EMIT3(0xC1, add_1reg(0xE8, dreg_hi), val);
-
-		/* IA32_ECX = 32 - val */
-		/* mov ecx,val */
-		EMIT2(0xB1, val);
-		/* movzx ecx,ecx */
-		EMIT3(0x0F, 0xB6, add_2reg(0xC0, IA32_ECX, IA32_ECX));
-		/* neg ecx */
-		EMIT2(0xF7, add_1reg(0xD8, IA32_ECX));
-		/* add ecx,32 */
-		EMIT3(0x83, add_1reg(0xC0, IA32_ECX), 32);
-
-		/* shl ebx,cl */
-		EMIT2(0xD3, add_1reg(0xE0, IA32_EBX));
-		/* or dreg_lo,ebx */
-		EMIT2(0x09, add_2reg(0xC0, dreg_lo, IA32_EBX));
 	} else if (val >= 32 && val < 64) {
 		u32 value = val - 32;
 
@@ -1025,27 +991,10 @@ static inline void emit_ia32_arsh_i64(const u8 dst[], const u32 val,
 	}
 	/* Do RSH operation */
 	if (val < 32) {
-		/* shr dreg_lo,imm8 */
-		EMIT3(0xC1, add_1reg(0xE8, dreg_lo), val);
-		/* mov ebx,dreg_hi */
-		EMIT2(0x8B, add_2reg(0xC0, dreg_hi, IA32_EBX));
+		/* shrd dreg_lo,dreg_hi,imm8 */
+		EMIT4(0x0F, 0xAC, add_2reg(0xC0, dreg_lo, dreg_hi), val);
 		/* ashr dreg_hi,imm8 */
 		EMIT3(0xC1, add_1reg(0xF8, dreg_hi), val);
-
-		/* IA32_ECX = 32 - val */
-		/* mov ecx,val */
-		EMIT2(0xB1, val);
-		/* movzx ecx,ecx */
-		EMIT3(0x0F, 0xB6, add_2reg(0xC0, IA32_ECX, IA32_ECX));
-		/* neg ecx */
-		EMIT2(0xF7, add_1reg(0xD8, IA32_ECX));
-		/* add ecx,32 */
-		EMIT3(0x83, add_1reg(0xC0, IA32_ECX), 32);
-
-		/* shl ebx,cl */
-		EMIT2(0xD3, add_1reg(0xE0, IA32_EBX));
-		/* or dreg_lo,ebx */
-		EMIT2(0x09, add_2reg(0xC0, dreg_lo, IA32_EBX));
 	} else if (val >= 32 && val < 64) {
 		u32 value = val - 32;
 
-- 
2.20.1