From: Roland McGrath Date: Tue, 14 Sep 2010 19:22:58 +0000 (-0700) Subject: x86-64, compat: Retruncate rax after ia32 syscall entry tracing X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=eefdca043e8391dcd719711716492063030b55ac;p=linux-beck.git x86-64, compat: Retruncate rax after ia32 syscall entry tracing In commit d4d6715, we reopened an old hole for a 64-bit ptracer touching a 32-bit tracee in system call entry. A %rax value set via ptrace at the entry tracing stop gets used whole as a 32-bit syscall number, while we only check the low 32 bits for validity. Fix it by truncating %rax back to 32 bits after syscall_trace_enter, in addition to testing the full 64 bits as has already been added. Reported-by: Ben Hawkes Signed-off-by: Roland McGrath Signed-off-by: H. Peter Anvin --- diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S index 84e3a4ef9719..518bb99c3394 100644 --- a/arch/x86/ia32/ia32entry.S +++ b/arch/x86/ia32/ia32entry.S @@ -50,7 +50,12 @@ /* * Reload arg registers from stack in case ptrace changed them. * We don't reload %eax because syscall_trace_enter() returned - * the value it wants us to use in the table lookup. + * the %rax value we should see. Instead, we just truncate that + * value to 32 bits again as we did on entry from user mode. + * If it's a new value set by user_regset during entry tracing, + * this matches the normal truncation of the user-mode value. + * If it's -1 to make us punt the syscall, then (u32)-1 is still + * an appropriately invalid value. */ .macro LOAD_ARGS32 offset, _r9=0 .if \_r9 @@ -60,6 +65,7 @@ movl \offset+48(%rsp),%edx movl \offset+56(%rsp),%esi movl \offset+64(%rsp),%edi + movl %eax,%eax /* zero extension */ .endm .macro CFI_STARTPROC32 simple