netdev - [PATCH RESEND bpf v2 2/2] x86/bpf: Fix IP for relocating call depth accounting

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Message-ID: <20240401185821.224068-3-ubizjak@gmail.com>
Date: Mon,  1 Apr 2024 20:55:30 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: x86@...nel.org,
	bpf@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Joan Bruguera Micó <joanbrugueram@...il.com>,
	Uros Bizjak <ubizjak@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH RESEND bpf v2 2/2] x86/bpf: Fix IP for relocating call depth accounting

From: Joan Bruguera Micó <joanbrugueram@...il.com>

The commit:

  59bec00ace28 ("x86/percpu: Introduce %rip-relative addressing to PER_CPU_VAR()")

made PER_CPU_VAR() to use rip-relative addressing, hence
INCREMENT_CALL_DEPTH macro and skl_call_thunk_template got rip-relative
asm code inside of it. A follow up commit:

  17bce3b2ae2d ("x86/callthunks: Handle %rip-relative relocations in call thunk template")

changed x86_call_depth_emit_accounting() to use apply_relocation(),
but mistakenly assumed that the code is being patched in-place (where
the destination of the relocation matches the address of the code),
using *pprog as the destination ip. This is not true for the call depth
accounting, emitted by the BPF JIT, so the calculated address was wrong,
JIT-ed BPF progs on kernels with call depth tracking got broken and
usually caused a page fault.

Pass the destination IP when the BPF JIT emits call depth accounting.

Fixes: 17bce3b2ae2d ("x86/callthunks: Handle %rip-relative relocations in call thunk template")
Signed-off-by: Joan Bruguera Micó <joanbrugueram@...il.com>
Reviewed-by: Uros Bizjak <ubizjak@...il.com>
Acked-by: Ingo Molnar <mingo@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
---
v2: Add more details to the commit message.
---
 arch/x86/include/asm/alternative.h |  4 ++--
 arch/x86/kernel/callthunks.c       |  4 ++--
 arch/x86/net/bpf_jit_comp.c        | 19 ++++++++-----------
 3 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index fcd20c6dc7f9..67b68d0d17d1 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -117,7 +117,7 @@ extern void callthunks_patch_builtin_calls(void);
 extern void callthunks_patch_module_calls(struct callthunk_sites *sites,
 					  struct module *mod);
 extern void *callthunks_translate_call_dest(void *dest);
-extern int x86_call_depth_emit_accounting(u8 **pprog, void *func);
+extern int x86_call_depth_emit_accounting(u8 **pprog, void *func, void *ip);
 #else
 static __always_inline void callthunks_patch_builtin_calls(void) {}
 static __always_inline void
@@ -128,7 +128,7 @@ static __always_inline void *callthunks_translate_call_dest(void *dest)
 	return dest;
 }
 static __always_inline int x86_call_depth_emit_accounting(u8 **pprog,
-							  void *func)
+							  void *func, void *ip)
 {
 	return 0;
 }
diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index 30335182b6b0..e92ff0c11db8 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -314,7 +314,7 @@ static bool is_callthunk(void *addr)
 	return !bcmp(pad, insn_buff, tmpl_size);
 }
 
-int x86_call_depth_emit_accounting(u8 **pprog, void *func)
+int x86_call_depth_emit_accounting(u8 **pprog, void *func, void *ip)
 {
 	unsigned int tmpl_size = SKL_TMPL_SIZE;
 	u8 insn_buff[MAX_PATCH_LEN];
@@ -327,7 +327,7 @@ int x86_call_depth_emit_accounting(u8 **pprog, void *func)
 		return 0;
 
 	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
-	apply_relocation(insn_buff, tmpl_size, *pprog,
+	apply_relocation(insn_buff, tmpl_size, ip,
 			 skl_call_thunk_template, tmpl_size);
 
 	memcpy(*pprog, insn_buff, tmpl_size);
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index e55745f512e1..df5fac428408 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -480,7 +480,7 @@ static int emit_call(u8 **pprog, void *func, void *ip)
 static int emit_rsb_call(u8 **pprog, void *func, void *ip)
 {
 	OPTIMIZER_HIDE_VAR(func);
-	ip += x86_call_depth_emit_accounting(pprog, func);
+	ip += x86_call_depth_emit_accounting(pprog, func, ip);
 	return emit_patch(pprog, func, ip, 0xE8);
 }
 
@@ -1972,20 +1972,17 @@ st:			if (is_imm8(insn->off))
 
 			/* call */
 		case BPF_JMP | BPF_CALL: {
-			int offs;
+			u8 *ip = image + addrs[i - 1];
 
 			func = (u8 *) __bpf_call_base + imm32;
 			if (tail_call_reachable) {
 				RESTORE_TAIL_CALL_CNT(bpf_prog->aux->stack_depth);
-				if (!imm32)
-					return -EINVAL;
-				offs = 7 + x86_call_depth_emit_accounting(&prog, func);
-			} else {
-				if (!imm32)
-					return -EINVAL;
-				offs = x86_call_depth_emit_accounting(&prog, func);
+				ip += 7;
 			}
-			if (emit_call(&prog, func, image + addrs[i - 1] + offs))
+			if (!imm32)
+				return -EINVAL;
+			ip += x86_call_depth_emit_accounting(&prog, func, ip);
+			if (emit_call(&prog, func, ip))
 				return -EINVAL;
 			break;
 		}
@@ -2835,7 +2832,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
 		 * Direct-call fentry stub, as such it needs accounting for the
 		 * __fentry__ call.
 		 */
-		x86_call_depth_emit_accounting(&prog, NULL);
+		x86_call_depth_emit_accounting(&prog, NULL, image);
 	}
 	EMIT1(0x55);		 /* push rbp */
 	EMIT3(0x48, 0x89, 0xE5); /* mov rbp, rsp */
-- 
2.42.0