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List:       linux-stable-commits
Subject:    Patch "bpf, x86_32: Fix clobbering of dst for BPF_JSET" has been added to the 5.6-stable tree
From:       <gregkh () linuxfoundation ! org>
Date:       2020-04-30 15:09:46
Message-ID: 1588259386191160 () kroah ! com
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This is a note to let you know that I've just added the patch titled

    bpf, x86_32: Fix clobbering of dst for BPF_JSET

to the 5.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpf-x86_32-fix-clobbering-of-dst-for-bpf_jset.patch
and it can be found in the queue-5.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From 50fe7ebb6475711c15b3397467e6424e20026d94 Mon Sep 17 00:00:00 2001
From: Luke Nelson <lukenels@cs.washington.edu>
Date: Wed, 22 Apr 2020 10:36:30 -0700
Subject: bpf, x86_32: Fix clobbering of dst for BPF_JSET

From: Luke Nelson <lukenels@cs.washington.edu>

commit 50fe7ebb6475711c15b3397467e6424e20026d94 upstream.

The current JIT clobbers the destination register for BPF_JSET BPF_X
and BPF_K by using "and" and "or" instructions. This is fine when the
destination register is a temporary loaded from a register stored on
the stack but not otherwise.

This patch fixes the problem (for both BPF_K and BPF_X) by always loading
the destination register into temporaries since BPF_JSET should not
modify the destination register.

This bug may not be currently triggerable as BPF_REG_AX is the only
register not stored on the stack and the verifier uses it in a limited
way.

Fixes: 03f5781be2c7b ("bpf, x86_32: add eBPF JIT compiler for ia32")
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Wang YanQing <udknight@gmail.com>
Link: https://lore.kernel.org/bpf/20200422173630.8351-2-luke.r.nels@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/net/bpf_jit_comp32.c |   22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

--- a/arch/x86/net/bpf_jit_comp32.c
+++ b/arch/x86/net/bpf_jit_comp32.c
@@ -2015,8 +2015,8 @@ static int do_jit(struct bpf_prog *bpf_p
 		case BPF_JMP | BPF_JSET | BPF_X:
 		case BPF_JMP32 | BPF_JSET | BPF_X: {
 			bool is_jmp64 = BPF_CLASS(insn->code) == BPF_JMP;
-			u8 dreg_lo = dstk ? IA32_EAX : dst_lo;
-			u8 dreg_hi = dstk ? IA32_EDX : dst_hi;
+			u8 dreg_lo = IA32_EAX;
+			u8 dreg_hi = IA32_EDX;
 			u8 sreg_lo = sstk ? IA32_ECX : src_lo;
 			u8 sreg_hi = sstk ? IA32_EBX : src_hi;
 
@@ -2028,6 +2028,13 @@ static int do_jit(struct bpf_prog *bpf_p
 					      add_2reg(0x40, IA32_EBP,
 						       IA32_EDX),
 					      STACK_VAR(dst_hi));
+			} else {
+				/* mov dreg_lo,dst_lo */
+				EMIT2(0x89, add_2reg(0xC0, dreg_lo, dst_lo));
+				if (is_jmp64)
+					/* mov dreg_hi,dst_hi */
+					EMIT2(0x89,
+					      add_2reg(0xC0, dreg_hi, dst_hi));
 			}
 
 			if (sstk) {
@@ -2052,8 +2059,8 @@ static int do_jit(struct bpf_prog *bpf_p
 		case BPF_JMP | BPF_JSET | BPF_K:
 		case BPF_JMP32 | BPF_JSET | BPF_K: {
 			bool is_jmp64 = BPF_CLASS(insn->code) == BPF_JMP;
-			u8 dreg_lo = dstk ? IA32_EAX : dst_lo;
-			u8 dreg_hi = dstk ? IA32_EDX : dst_hi;
+			u8 dreg_lo = IA32_EAX;
+			u8 dreg_hi = IA32_EDX;
 			u8 sreg_lo = IA32_ECX;
 			u8 sreg_hi = IA32_EBX;
 			u32 hi;
@@ -2066,6 +2073,13 @@ static int do_jit(struct bpf_prog *bpf_p
 					      add_2reg(0x40, IA32_EBP,
 						       IA32_EDX),
 					      STACK_VAR(dst_hi));
+			} else {
+				/* mov dreg_lo,dst_lo */
+				EMIT2(0x89, add_2reg(0xC0, dreg_lo, dst_lo));
+				if (is_jmp64)
+					/* mov dreg_hi,dst_hi */
+					EMIT2(0x89,
+					      add_2reg(0xC0, dreg_hi, dst_hi));
 			}
 
 			/* mov ecx,imm32 */


Patches currently in stable-queue which might be from lukenels@cs.washington.edu are

queue-5.6/bpf-x86_32-fix-incorrect-encoding-in-bpf_ldx-zero-extension.patch
queue-5.6/bpf-x86_32-fix-clobbering-of-dst-for-bpf_jset.patch
queue-5.6/bpf-x86-fix-encoding-for-lower-8-bit-registers-in-bpf_stx-bpf_b.patch
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