From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Fri, 18 Apr 2025 12:49:59 +0000 (-0300)
Subject: x86_64: Fix UB on plt rewrite
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8cc687cbacf4f2b9950e7ac4b3738e0add136098;p=thirdparty%2Fglibc.git

x86_64: Fix UB on plt rewrite

The elf/tst-plt-rewrite2 and elf/tst-plt-rewrite2 triggers the
failures with ubsan:

UBSAN: Undefined behaviour in ../sysdeps/x86_64/dl-machine.h:637:39 store to misaligned address 0x00007adb50230021 for type 'uint32_t'
---

diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
index 572a1a7395..3799894589 100644
--- a/sysdeps/x86_64/dl-machine.h
+++ b/sysdeps/x86_64/dl-machine.h
@@ -633,7 +633,7 @@ x86_64_rewrite_plt (struct link_map *map, ElfW(Addr) plt_rewrite)
 
 	    /* Write out direct branch.  */
 	    *(uint8_t *) branch_start = JMP32_INSN_OPCODE;
-	    *(uint32_t *) (branch_start + 1) = disp;
+	    memcpy ((void *)(branch_start + 1), &disp, sizeof (uint32_t));
 	  }
 	else
 	  {