Commit 68a8357e authored by Luke Nelson's avatar Luke Nelson Committed by Daniel Borkmann
Browse files

bpf, x32: Fix bug with ALU64 {LSH, RSH, ARSH} BPF_X shift by 0 



The current x32 BPF JIT for shift operations is not correct when the
shift amount in a register is 0. The expected behavior is a no-op, whereas
the current implementation changes bits in the destination register.

The following example demonstrates the bug. The expected result of this
program is 1, but the current JITed code returns 2.

  r0 = 1
  r1 = 1
  r2 = 0
  r1 <<= r2
  if r1 == 1 goto end
  r0 = 2
end:
  exit

The bug is caused by an incorrect assumption by the JIT that a shift by
32 clear the register. On x32 however, shifts use the lower 5 bits of
the source, making a shift by 32 equivalent to a shift by 0.

This patch fixes the bug using double-precision shifts, which also
simplifies the code.

Fixes: 03f5781b ("bpf, x86_32: add eBPF JIT compiler for ia32")
Co-developed-by: default avatarXi Wang <xi.wang@gmail.com>
Signed-off-by: default avatarXi Wang <xi.wang@gmail.com>
Signed-off-by: default avatarLuke Nelson <luke.r.nels@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 0472301a

arch/x86/net/bpf_jit_comp32.c

+23 −198
Original line number Diff line number Diff line
@@ -724,9 +724,6 @@ static inline void emit_ia32_lsh_r64(const u8 dst[], const u8 src[], 
{

	u8 *prog = *pprog;

	int cnt = 0;

	static int jmp_label1 = -1;

	static int jmp_label2 = -1;

	static int jmp_label3 = -1;

	u8 dreg_lo = dstk ? IA32_EAX : dst_lo;

	u8 dreg_hi = dstk ? IA32_EDX : dst_hi;
@@ -745,79 +742,23 @@ static inline void emit_ia32_lsh_r64(const u8 dst[], const u8 src[], 
		/* mov ecx,src_lo */

		EMIT2(0x8B, add_2reg(0xC0, src_lo, IA32_ECX));



	/* cmp ecx,32 */

	EMIT3(0x83, add_1reg(0xF8, IA32_ECX), 32);

	/* Jumps when >= 32 */

	if (is_imm8(jmp_label(jmp_label1, 2)))

		EMIT2(IA32_JAE, jmp_label(jmp_label1, 2));

	else

		EMIT2_off32(0x0F, IA32_JAE + 0x10, jmp_label(jmp_label1, 6));



	/* < 32 */

	/* shl dreg_hi,cl */

	EMIT2(0xD3, add_1reg(0xE0, dreg_hi));

	/* mov ebx,dreg_lo */

	EMIT2(0x8B, add_2reg(0xC0, dreg_lo, IA32_EBX));

	/* shld dreg_hi,dreg_lo,cl */

	EMIT3(0x0F, 0xA5, add_2reg(0xC0, dreg_hi, dreg_lo));

	/* shl dreg_lo,cl */

	EMIT2(0xD3, add_1reg(0xE0, dreg_lo));



	/* IA32_ECX = -IA32_ECX + 32 */

	/* neg ecx */

	EMIT2(0xF7, add_1reg(0xD8, IA32_ECX));

	/* add ecx,32 */

	EMIT3(0x83, add_1reg(0xC0, IA32_ECX), 32);

	/* if ecx >= 32, mov dreg_lo into dreg_hi and clear dreg_lo */



	/* shr ebx,cl */

	EMIT2(0xD3, add_1reg(0xE8, IA32_EBX));

	/* or dreg_hi,ebx */

	EMIT2(0x09, add_2reg(0xC0, dreg_hi, IA32_EBX));



	/* goto out; */

	if (is_imm8(jmp_label(jmp_label3, 2)))

		EMIT2(0xEB, jmp_label(jmp_label3, 2));

	else

		EMIT1_off32(0xE9, jmp_label(jmp_label3, 5));



	/* >= 32 */

	if (jmp_label1 == -1)

		jmp_label1 = cnt;



	/* cmp ecx,64 */

	EMIT3(0x83, add_1reg(0xF8, IA32_ECX), 64);

	/* Jumps when >= 64 */

	if (is_imm8(jmp_label(jmp_label2, 2)))

		EMIT2(IA32_JAE, jmp_label(jmp_label2, 2));

	else

		EMIT2_off32(0x0F, IA32_JAE + 0x10, jmp_label(jmp_label2, 6));

	/* cmp ecx,32 */

	EMIT3(0x83, add_1reg(0xF8, IA32_ECX), 32);

	/* skip the next two instructions (4 bytes) when < 32 */

	EMIT2(IA32_JB, 4);



	/* >= 32 && < 64 */

	/* sub ecx,32 */

	EMIT3(0x83, add_1reg(0xE8, IA32_ECX), 32);

	/* shl dreg_lo,cl */

	EMIT2(0xD3, add_1reg(0xE0, dreg_lo));

	/* mov dreg_hi,dreg_lo */

	EMIT2(0x89, add_2reg(0xC0, dreg_hi, dreg_lo));



	/* xor dreg_lo,dreg_lo */

	EMIT2(0x33, add_2reg(0xC0, dreg_lo, dreg_lo));



	/* goto out; */

	if (is_imm8(jmp_label(jmp_label3, 2)))

		EMIT2(0xEB, jmp_label(jmp_label3, 2));

	else

		EMIT1_off32(0xE9, jmp_label(jmp_label3, 5));



	/* >= 64 */

	if (jmp_label2 == -1)

		jmp_label2 = cnt;

	/* xor dreg_lo,dreg_lo */

	EMIT2(0x33, add_2reg(0xC0, dreg_lo, dreg_lo));

	/* xor dreg_hi,dreg_hi */

	EMIT2(0x33, add_2reg(0xC0, dreg_hi, dreg_hi));



	if (jmp_label3 == -1)

		jmp_label3 = cnt;



	if (dstk) {

		/* mov dword ptr [ebp+off],dreg_lo */

		EMIT3(0x89, add_2reg(0x40, IA32_EBP, dreg_lo),
@@ -836,9 +777,6 @@ static inline void emit_ia32_arsh_r64(const u8 dst[], const u8 src[], 
{

	u8 *prog = *pprog;

	int cnt = 0;

	static int jmp_label1 = -1;

	static int jmp_label2 = -1;

	static int jmp_label3 = -1;

	u8 dreg_lo = dstk ? IA32_EAX : dst_lo;

	u8 dreg_hi = dstk ? IA32_EDX : dst_hi;
@@ -857,79 +795,23 @@ static inline void emit_ia32_arsh_r64(const u8 dst[], const u8 src[], 
		/* mov ecx,src_lo */

		EMIT2(0x8B, add_2reg(0xC0, src_lo, IA32_ECX));



	/* cmp ecx,32 */

	EMIT3(0x83, add_1reg(0xF8, IA32_ECX), 32);

	/* Jumps when >= 32 */

	if (is_imm8(jmp_label(jmp_label1, 2)))

		EMIT2(IA32_JAE, jmp_label(jmp_label1, 2));

	else

		EMIT2_off32(0x0F, IA32_JAE + 0x10, jmp_label(jmp_label1, 6));



	/* < 32 */

	/* lshr dreg_lo,cl */

	EMIT2(0xD3, add_1reg(0xE8, dreg_lo));

	/* mov ebx,dreg_hi */

	EMIT2(0x8B, add_2reg(0xC0, dreg_hi, IA32_EBX));

	/* ashr dreg_hi,cl */

	/* shrd dreg_lo,dreg_hi,cl */

	EMIT3(0x0F, 0xAD, add_2reg(0xC0, dreg_lo, dreg_hi));

	/* sar dreg_hi,cl */

	EMIT2(0xD3, add_1reg(0xF8, dreg_hi));



	/* IA32_ECX = -IA32_ECX + 32 */

	/* 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));



	/* goto out; */

	if (is_imm8(jmp_label(jmp_label3, 2)))

		EMIT2(0xEB, jmp_label(jmp_label3, 2));

	else

		EMIT1_off32(0xE9, jmp_label(jmp_label3, 5));

	/* if ecx >= 32, mov dreg_hi to dreg_lo and set/clear dreg_hi depending on sign */



	/* >= 32 */

	if (jmp_label1 == -1)

		jmp_label1 = cnt;



	/* cmp ecx,64 */

	EMIT3(0x83, add_1reg(0xF8, IA32_ECX), 64);

	/* Jumps when >= 64 */

	if (is_imm8(jmp_label(jmp_label2, 2)))

		EMIT2(IA32_JAE, jmp_label(jmp_label2, 2));

	else

		EMIT2_off32(0x0F, IA32_JAE + 0x10, jmp_label(jmp_label2, 6));

	/* cmp ecx,32 */

	EMIT3(0x83, add_1reg(0xF8, IA32_ECX), 32);

	/* skip the next two instructions (5 bytes) when < 32 */

	EMIT2(IA32_JB, 5);



	/* >= 32 && < 64 */

	/* sub ecx,32 */

	EMIT3(0x83, add_1reg(0xE8, IA32_ECX), 32);

	/* ashr dreg_hi,cl */

	EMIT2(0xD3, add_1reg(0xF8, dreg_hi));

	/* mov dreg_lo,dreg_hi */

	EMIT2(0x89, add_2reg(0xC0, dreg_lo, dreg_hi));



	/* ashr dreg_hi,imm8 */

	/* sar dreg_hi,31 */

	EMIT3(0xC1, add_1reg(0xF8, dreg_hi), 31);



	/* goto out; */

	if (is_imm8(jmp_label(jmp_label3, 2)))

		EMIT2(0xEB, jmp_label(jmp_label3, 2));

	else

		EMIT1_off32(0xE9, jmp_label(jmp_label3, 5));



	/* >= 64 */

	if (jmp_label2 == -1)

		jmp_label2 = cnt;

	/* ashr dreg_hi,imm8 */

	EMIT3(0xC1, add_1reg(0xF8, dreg_hi), 31);

	/* mov dreg_lo,dreg_hi */

	EMIT2(0x89, add_2reg(0xC0, dreg_lo, dreg_hi));



	if (jmp_label3 == -1)

		jmp_label3 = cnt;



	if (dstk) {

		/* mov dword ptr [ebp+off],dreg_lo */

		EMIT3(0x89, add_2reg(0x40, IA32_EBP, dreg_lo),
@@ -948,9 +830,6 @@ static inline void emit_ia32_rsh_r64(const u8 dst[], const u8 src[], bool dstk, 
{

	u8 *prog = *pprog;

	int cnt = 0;

	static int jmp_label1 = -1;

	static int jmp_label2 = -1;

	static int jmp_label3 = -1;

	u8 dreg_lo = dstk ? IA32_EAX : dst_lo;

	u8 dreg_hi = dstk ? IA32_EDX : dst_hi;
@@ -969,77 +848,23 @@ static inline void emit_ia32_rsh_r64(const u8 dst[], const u8 src[], bool dstk, 
		/* mov ecx,src_lo */

		EMIT2(0x8B, add_2reg(0xC0, src_lo, IA32_ECX));



	/* cmp ecx,32 */

	EMIT3(0x83, add_1reg(0xF8, IA32_ECX), 32);

	/* Jumps when >= 32 */

	if (is_imm8(jmp_label(jmp_label1, 2)))

		EMIT2(IA32_JAE, jmp_label(jmp_label1, 2));

	else

		EMIT2_off32(0x0F, IA32_JAE + 0x10, jmp_label(jmp_label1, 6));



	/* < 32 */

	/* lshr dreg_lo,cl */

	EMIT2(0xD3, add_1reg(0xE8, dreg_lo));

	/* mov ebx,dreg_hi */

	EMIT2(0x8B, add_2reg(0xC0, dreg_hi, IA32_EBX));

	/* shrd dreg_lo,dreg_hi,cl */

	EMIT3(0x0F, 0xAD, add_2reg(0xC0, dreg_lo, dreg_hi));

	/* shr dreg_hi,cl */

	EMIT2(0xD3, add_1reg(0xE8, dreg_hi));



	/* IA32_ECX = -IA32_ECX + 32 */

	/* neg ecx */

	EMIT2(0xF7, add_1reg(0xD8, IA32_ECX));

	/* add ecx,32 */

	EMIT3(0x83, add_1reg(0xC0, IA32_ECX), 32);

	/* if ecx >= 32, mov dreg_hi to dreg_lo and clear dreg_hi */



	/* shl ebx,cl */

	EMIT2(0xD3, add_1reg(0xE0, IA32_EBX));

	/* or dreg_lo,ebx */

	EMIT2(0x09, add_2reg(0xC0, dreg_lo, IA32_EBX));



	/* goto out; */

	if (is_imm8(jmp_label(jmp_label3, 2)))

		EMIT2(0xEB, jmp_label(jmp_label3, 2));

	else

		EMIT1_off32(0xE9, jmp_label(jmp_label3, 5));



	/* >= 32 */

	if (jmp_label1 == -1)

		jmp_label1 = cnt;

	/* cmp ecx,64 */

	EMIT3(0x83, add_1reg(0xF8, IA32_ECX), 64);

	/* Jumps when >= 64 */

	if (is_imm8(jmp_label(jmp_label2, 2)))

		EMIT2(IA32_JAE, jmp_label(jmp_label2, 2));

	else

		EMIT2_off32(0x0F, IA32_JAE + 0x10, jmp_label(jmp_label2, 6));

	/* cmp ecx,32 */

	EMIT3(0x83, add_1reg(0xF8, IA32_ECX), 32);

	/* skip the next two instructions (4 bytes) when < 32 */

	EMIT2(IA32_JB, 4);



	/* >= 32 && < 64 */

	/* sub ecx,32 */

	EMIT3(0x83, add_1reg(0xE8, IA32_ECX), 32);

	/* shr dreg_hi,cl */

	EMIT2(0xD3, add_1reg(0xE8, dreg_hi));

	/* mov dreg_lo,dreg_hi */

	EMIT2(0x89, add_2reg(0xC0, dreg_lo, dreg_hi));

	/* xor dreg_hi,dreg_hi */

	EMIT2(0x33, add_2reg(0xC0, dreg_hi, dreg_hi));



	/* goto out; */

	if (is_imm8(jmp_label(jmp_label3, 2)))

		EMIT2(0xEB, jmp_label(jmp_label3, 2));

	else

		EMIT1_off32(0xE9, jmp_label(jmp_label3, 5));



	/* >= 64 */

	if (jmp_label2 == -1)

		jmp_label2 = cnt;

	/* xor dreg_lo,dreg_lo */

	EMIT2(0x33, add_2reg(0xC0, dreg_lo, dreg_lo));

	/* xor dreg_hi,dreg_hi */

	EMIT2(0x33, add_2reg(0xC0, dreg_hi, dreg_hi));



	if (jmp_label3 == -1)

		jmp_label3 = cnt;



	if (dstk) {

		/* mov dword ptr [ebp+off],dreg_lo */

		EMIT3(0x89, add_2reg(0x40, IA32_EBP, dreg_lo),

CRA Git | Maintained and supported by SUSTech CRA and CCSE