From 4cc06bef26c3573309086bec4472cc9151b0379e Mon Sep 17 00:00:00 2001 From: Michael Chang Date: Mon, 1 Feb 2021 20:14:12 +0800 Subject: [PATCH] emu: fix executable stack marking The gcc by default assumes executable stack is required if the source object file doesn't have .note.GNU-stack section in place. If any of the source objects doesn't incorporate the GNU-stack note, the resulting program will have executable stack flag set in PT_GNU_STACK program header to instruct program loader or kernel to set up the exeutable stack when program loads to memory. Usually the .note.GNU-stack section will be generated by gcc automatically if it finds that executable stack is not required. However it doesn't take care of generating .note.GNU-stack section for those object files built from assembler sources. This leads to unnecessary risk of security of exploiting the executable stack because those assembler sources don't actually require stack to be executable to work. The grub-emu and grub-emu-lite are found to flag stack as executable revealed by execstack tool. $ mkdir -p build-emu && cd build-emu $ ../configure --with-platform=emu && make $ execstack -q grub-core/grub-emu grub-core/grub-emu-lite X grub-core/grub-emu X grub-core/grub-emu-lite This patch will add the missing GNU-stack note to the assembler source used by both utilities, therefore the result doesn't count on gcc default behavior and the executable stack is disabled. $ execstack -q grub-core/grub-emu grub-core/grub-emu-lite - grub-core/grub-emu - grub-core/grub-emu-lite Signed-off-by: Michael Chang --- grub-core/kern/emu/cache_s.S | 5 +++++ grub-core/lib/setjmp.S | 4 ++++ 2 files changed, 9 insertions(+) Index: grub-2.04/grub-core/kern/emu/cache_s.S =================================================================== --- grub-2.04.orig/grub-core/kern/emu/cache_s.S +++ grub-2.04/grub-core/kern/emu/cache_s.S @@ -2,6 +2,11 @@ #error "This source is only meant for grub-emu platform" #endif +/* An executable stack is not required for these functions */ +#if defined (__linux__) && defined (__ELF__) +.section .note.GNU-stack,"",%progbits +#endif + #if defined(__i386__) || defined(__x86_64__) /* Nothing is necessary. */ #elif defined(__sparc__) Index: grub-2.04/grub-core/lib/setjmp.S =================================================================== --- grub-2.04.orig/grub-core/lib/setjmp.S +++ grub-2.04/grub-core/lib/setjmp.S @@ -1,3 +1,7 @@ +/* An executable stack is not required for these functions */ +#if defined (__linux__) && defined (__ELF__) +.section .note.GNU-stack,"",%progbits +#endif #if defined(__i386__) #include "./i386/setjmp.S" #elif defined(__x86_64__)