linux-kernel - [PATCH 5.3 159/197] s390/kaslr: add support for R_390_GLOB

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Message-Id: <20191027203400.264805187@linuxfoundation.org>
Date:   Sun, 27 Oct 2019 22:01:17 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Heiko Carstens <heiko.carstens@...ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: [PATCH 5.3 159/197] s390/kaslr: add support for R_390_GLOB_DAT relocation type

From: Gerald Schaefer <gerald.schaefer@...ibm.com>

commit ac49303d9ef0ad98b79867a380ef23480e48870b upstream.

Commit "bpf: Process in-kernel BTF" in linux-next introduced an undefined
__weak symbol, which results in an R_390_GLOB_DAT relocation type. That
is not yet handled by the KASLR relocation code, and the kernel stops with
the message "Unknown relocation type".

Add code to detect and handle R_390_GLOB_DAT relocation types and undefined
symbols.

Fixes: 805bc0bc238f ("s390/kernel: build a relocatable kernel")
Cc: <stable@...r.kernel.org> # v5.2+
Acked-by: Heiko Carstens <heiko.carstens@...ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@...ibm.com>
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/s390/boot/startup.c               |   14 +++++++++++---
 arch/s390/kernel/machine_kexec_reloc.c |    1 +
 2 files changed, 12 insertions(+), 3 deletions(-)

--- a/arch/s390/boot/startup.c
+++ b/arch/s390/boot/startup.c
@@ -101,10 +101,18 @@ static void handle_relocs(unsigned long
 	dynsym = (Elf64_Sym *) vmlinux.dynsym_start;
 	for (rela = rela_start; rela < rela_end; rela++) {
 		loc = rela->r_offset + offset;
-		val = rela->r_addend + offset;
+		val = rela->r_addend;
 		r_sym = ELF64_R_SYM(rela->r_info);
-		if (r_sym)
-			val += dynsym[r_sym].st_value;
+		if (r_sym) {
+			if (dynsym[r_sym].st_shndx != SHN_UNDEF)
+				val += dynsym[r_sym].st_value + offset;
+		} else {
+			/*
+			 * 0 == undefined symbol table index (STN_UNDEF),
+			 * used for R_390_RELATIVE, only add KASLR offset
+			 */
+			val += offset;
+		}
 		r_type = ELF64_R_TYPE(rela->r_info);
 		rc = arch_kexec_do_relocs(r_type, (void *) loc, val, 0);
 		if (rc)
--- a/arch/s390/kernel/machine_kexec_reloc.c
+++ b/arch/s390/kernel/machine_kexec_reloc.c
@@ -27,6 +27,7 @@ int arch_kexec_do_relocs(int r_type, voi
 		*(u32 *)loc = val;
 		break;
 	case R_390_64:		/* Direct 64 bit.  */
+	case R_390_GLOB_DAT:
 		*(u64 *)loc = val;
 		break;
 	case R_390_PC16:	/* PC relative 16 bit.	*/