diff options
Diffstat (limited to 'results/classifier/gemma3:27b/instruction/1613817')
| -rw-r--r-- | results/classifier/gemma3:27b/instruction/1613817 | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/results/classifier/gemma3:27b/instruction/1613817 b/results/classifier/gemma3:27b/instruction/1613817 new file mode 100644 index 00000000..f631772b --- /dev/null +++ b/results/classifier/gemma3:27b/instruction/1613817 @@ -0,0 +1,59 @@ + + + +x86: ret, lret and iret with noncanonical IP saves wrong IP on the exception stack + +This test program: + +# compile with: gcc -nostartfiles -nostdlib +_start: .globl _start + mov %ss,%eax + push %rax + push %rsp + pushf + mov %cs,%eax + push %rax + mov $0x1234567812345678,%rax + push %rax +//qemu bug: ip=1234567812345678, should be ip=0000000000400abc: + iretq +1: + jmp 1b + +should segfault on IRET instruction because return address on stack is invalid +(it is not canonical). And it does, both on native CPU and in qemu. +But there is a difference: on native CPU, it fails before instruction is executed, +IOW: saved IP points to the failed IRET: + +# strace -i ./bad_ip_in_iret +[00007fa609805d57] execve("./bad_ip_in_iret", ["./bad_ip_in_iret"], [/* 54 vars */]) = 0 +[00000000004000e7] --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=0} --- + ^^^^^^^^^^^^^^^^-NOTE THIS +[????????????????] +++ killed by SIGSEGV (core dumped) +++ + + +In qemu, evidently instruction succeeds, and then emulated CPU throws an exception because fetching instructions from non-canonical addresses is not allowed: + +/ # strace -i ./bad_ip_in_iret +[000000000041a790] execve("./bad_ip_in_iret", ["./bad_ip_in_iret"], [/* 5 vars */]) = 0 +[1234567812345678] --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=0} --- + ^^^^^^^^^^^^^^^^-NOTE THIS +[????????????????] +++ killed by SIGSEGV +++ +Segmentation fault + +Thus, the emulation is not the same as real CPU. + +This is not specific to IRET, the same happens with "far return" LRET, +and with ordinary RET instructions as well. +In qemu: + +/ # strace -i ./bad_ip_in_lret +[000000000041a790] execve("./bad_ip_in_lret", ["./bad_ip_in_lret"], [/* 5 vars */]) = 0 +[1234567812345678] --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=0} --- +[????????????????] +++ killed by SIGSEGV +++ +Segmentation fault +/ # strace -i ./bad_ip_in_ret +[000000000041a790] execve("./bad_ip_in_ret", ["./bad_ip_in_ret"], [/* 5 vars */]) = 0 +[1234567812345678] --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=0} --- +[????????????????] +++ killed by SIGSEGV +++ +Segmentation fault \ No newline at end of file |