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FAILED: patch "[PATCH] bpf, x86_32: Fix clobbering of dst for BPF_JSET" failed to apply to 4.19-stable tree

PATCH [email protected] 1 participant 1 message Apr 30, 2020

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Stable branch x86 BPF BPF JIT for x86 32-bit
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The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 50fe7ebb6475711c15b3397467e6424e20026d94 Mon Sep 17 00:00:00 2001
From: Luke Nelson <[email protected]>
Date: Wed, 22 Apr 2020 10:36:30 -0700
Subject: [PATCH] bpf, x86_32: Fix clobbering of dst for BPF_JSET

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 <[email protected]>
Signed-off-by Luke Nelson <[email protected]>
Signed-off-by Alexei Starovoitov <[email protected]>
Acked-by Wang YanQing <[email protected]>
Link https://lore.kernel.org/bpf/[email protected] open here
arch/x86/net/bpf_jit_comp32.c +18 -4
index cc9ad3892ea6..ba7d9ccfc662 100644
@@ -2015,8 +2015,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 		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_prog, int *addrs, u8 *image,
 					      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_prog, int *addrs, u8 *image,
 		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_prog, int *addrs, u8 *image,
 					      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 */