On Tue, Nov 16, 2021 at 7:20 PM H.J. Lu via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Add -mharden-sls= to mitigate against straight line speculation (SLS)
> for function return and indirect branch by adding an INT3 instruction
> after function return and indirect branch.
>
> gcc/
>
> PR target/102952
> * config/i386/i386-opts.h (harden_sls): New enum.
> * config/i386/i386.c (output_indirect_thunk): Mitigate against
> SLS for function return.
> (ix86_output_function_return): Likewise.
> (ix86_output_jmp_thunk_or_indirect): Mitigate against indirect
> branch.
> (ix86_output_indirect_jmp): Likewise.
> (ix86_output_call_insn): Likewise.
> * config/i386/i386.opt: Add -mharden-sls=.
> * doc/invoke.texi: Document -mharden-sls=.
>
> gcc/testsuite/
>
> PR target/102952
> * gcc.target/i386/harden-sls-1.c: New test.
> * gcc.target/i386/harden-sls-2.c: Likewise.
> * gcc.target/i386/harden-sls-3.c: Likewise.
> * gcc.target/i386/harden-sls-4.c: Likewise.
> ---
> gcc/config/i386/i386-opts.h | 7 +++++
> gcc/config/i386/i386.c | 30 ++++++++++++++++----
> gcc/config/i386/i386.opt | 20 +++++++++++++
> gcc/doc/invoke.texi | 10 ++++++-
> gcc/testsuite/gcc.target/i386/harden-sls-1.c | 14 +++++++++
> gcc/testsuite/gcc.target/i386/harden-sls-2.c | 14 +++++++++
> gcc/testsuite/gcc.target/i386/harden-sls-3.c | 14 +++++++++
> gcc/testsuite/gcc.target/i386/harden-sls-4.c | 14 +++++++++
> 8 files changed, 116 insertions(+), 7 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/i386/harden-sls-1.c
> create mode 100644 gcc/testsuite/gcc.target/i386/harden-sls-2.c
> create mode 100644 gcc/testsuite/gcc.target/i386/harden-sls-3.c
> create mode 100644 gcc/testsuite/gcc.target/i386/harden-sls-4.c
>
> diff --git a/gcc/config/i386/i386-opts.h b/gcc/config/i386/i386-opts.h
> index 04e4ad608fb..171d3106d0a 100644
> --- a/gcc/config/i386/i386-opts.h
> +++ b/gcc/config/i386/i386-opts.h
> @@ -121,4 +121,11 @@ enum instrument_return {
> instrument_return_nop5
> };
>
> +enum harden_sls {
> + harden_sls_none = 0,
> + harden_sls_return = 1 << 0,
> + harden_sls_indirect_branch = 1 << 1,
> + harden_sls_all = harden_sls_return | harden_sls_indirect_branch
> +};
> +
> #endif
> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> index cc9f9322fad..0a902d66321 100644
> --- a/gcc/config/i386/i386.c
> +++ b/gcc/config/i386/i386.c
> @@ -5914,6 +5914,8 @@ output_indirect_thunk (unsigned int regno)
> }
>
> fputs ("\tret\n", asm_out_file);
> + if ((ix86_harden_sls & harden_sls_return))
> + fputs ("\tint3\n", asm_out_file);
> }
>
> /* Output a funtion with a call and return thunk for indirect branch.
> @@ -15987,6 +15989,8 @@ ix86_output_jmp_thunk_or_indirect (const char
> *thunk_name, const int regno)
> fprintf (asm_out_file, "\tjmp\t");
> assemble_name (asm_out_file, thunk_name);
> putc ('\n', asm_out_file);
> + if ((ix86_harden_sls & harden_sls_indirect_branch))
> + fputs ("\tint3\n", asm_out_file);
> }
> else
> output_indirect_thunk (regno);
> @@ -16212,10 +16216,14 @@ ix86_output_indirect_jmp (rtx call_op)
> gcc_unreachable ();
>
> ix86_output_indirect_branch (call_op, "%0", true);
> - return "";
> + if ((ix86_harden_sls & harden_sls_indirect_branch))
> + return "int3";
> + else
> + return "";
> }
> else
> - return "%!jmp\t%A0";
> + return ((ix86_harden_sls & harden_sls_indirect_branch)
> + ? "%!jmp\t%A0\n\tint3" : "%!jmp\t%A0");
> }
Just change existing returns to fputs and end function with:
return (ix86_harden_sls & harden_sls_indirect_branch) ? "int3" : "";
> /* Output return instrumentation for current function if needed. */
> @@ -16283,10 +16291,15 @@ ix86_output_function_return (bool long_p)
> return "";
> }
>
> - if (!long_p)
> - return "%!ret";
> + if ((ix86_harden_sls & harden_sls_return))
> + return "%!ret\n\tint3";
> + else
> + {
> + if (!long_p)
> + return "%!ret";
>
> - return "rep%; ret";
> + return "rep%; ret";
> + }
> }
Also here.
>
> /* Output indirect function return. RET_OP is the function return
> @@ -16381,7 +16394,12 @@ ix86_output_call_insn (rtx_insn *insn, rtx call_op)
> if (output_indirect_p && !direct_p)
> ix86_output_indirect_branch (call_op, xasm, true);
> else
> - output_asm_insn (xasm, &call_op);
> + {
> + output_asm_insn (xasm, &call_op);
> + if (!direct_p
> + && (ix86_harden_sls & harden_sls_indirect_branch))
> + return "int3";
> + }
> return "";
> }
>
> diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> index b38ac13fc91..c5452c49597 100644
> --- a/gcc/config/i386/i386.opt
> +++ b/gcc/config/i386/i386.opt
> @@ -1121,6 +1121,26 @@ mrecord-return
> Target Var(ix86_flag_record_return) Init(0)
> Generate a __return_loc section pointing to all return instrumentation code.
>
> +mharden-sls=
> +Target RejectNegative Joined Enum(harden_sls) Var(ix86_harden_sls)
> Init(harden_sls_none)
> +Generate code to mitigate against straight line speculation.
> +
> +Enum
> +Name(harden_sls) Type(enum harden_sls)
> +Known choices for mitigation against straight line speculation with
> -mharden-sls=:
> +
> +EnumValue
> +Enum(harden_sls) String(none) Value(harden_sls_none)
> +
> +EnumValue
> +Enum(harden_sls) String(all) Value(harden_sls_all)
> +
> +EnumValue
> +Enum(harden_sls) String(return) Value(harden_sls_return)
> +
> +EnumValue
> +Enum(harden_sls) String(indirect-branch) Value(harden_sls_indirect_branch)
> +
> mavx512bf16
> Target Mask(ISA2_AVX512BF16) Var(ix86_isa_flags2) Save
> Support MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2, AVX512F and
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 6070288856c..f3b4b467765 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -1425,7 +1425,7 @@ See RS/6000 and PowerPC Options.
> -mstack-protector-guard-symbol=@var{symbol} @gol
> -mgeneral-regs-only -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop @gol
> -mindirect-branch=@var{choice} -mfunction-return=@var{choice} @gol
> --mindirect-branch-register -mneeded}
> +-mindirect-branch-register -mharden-sls=@var{choice} -mneeded}
>
> @emph{x86 Windows Options}
> @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol
> @@ -32382,6 +32382,14 @@ not be reachable in the large code model.
> @opindex mindirect-branch-register
> Force indirect call and jump via register.
>
> +@item -mharden-sls=@var{choice}
> +@opindex mharden-sls
> +Generate code to mitigate against straight line speculation (SLS) with
> +@var{choice}. The default is @samp{none} which disables all SLS
> +hardening. @samp{return} enables SLS hardening for function return.
> +@samp{indirect-branch} enables SLS hardening for indirect branch.
> +@samp{all} enables all SLS hardening.
> +
> @end table
>
> These @samp{-m} switches are supported in addition to the above
> diff --git a/gcc/testsuite/gcc.target/i386/harden-sls-1.c
> b/gcc/testsuite/gcc.target/i386/harden-sls-1.c
> new file mode 100644
> index 00000000000..6f70dc94a23
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/harden-sls-1.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mindirect-branch=thunk-extern -mharden-sls=all" } */
> +/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
> +
> +extern void foo (void);
> +
> +void
> +bar (void)
> +{
> + foo ();
> +}
> +
> +/* { dg-final { scan-assembler "jmp\[ \t\]+_?foo" } } */
> +/* { dg-final { scan-assembler-not {int3} } } */
> diff --git a/gcc/testsuite/gcc.target/i386/harden-sls-2.c
> b/gcc/testsuite/gcc.target/i386/harden-sls-2.c
> new file mode 100644
> index 00000000000..a7c59078d03
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/harden-sls-2.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mindirect-branch=thunk-extern -mharden-sls=all" } */
> +/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
> +
> +extern void (*fptr) (void);
> +
> +void
> +foo (void)
> +{
> + fptr ();
> +}
> +
> +/* { dg-final { scan-assembler "jmp\[ \t\]+_?__x86_indirect_thunk_(r|e)ax" }
> } */
> +/* { dg-final { scan-assembler-times "int3" 1 } } */
> diff --git a/gcc/testsuite/gcc.target/i386/harden-sls-3.c
> b/gcc/testsuite/gcc.target/i386/harden-sls-3.c
> new file mode 100644
> index 00000000000..1a6056b6d7b
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/harden-sls-3.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mindirect-branch=thunk -mharden-sls=all" } */
> +/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
> +
> +extern void (*fptr) (void);
> +
> +void
> +foo (void)
> +{
> + fptr ();
> +}
> +
> +/* { dg-final { scan-assembler "jmp\[ \t\]+_?__x86_indirect_thunk_(r|e)ax" }
> } */
> +/* { dg-final { scan-assembler-times "int3" 2 } } */
> diff --git a/gcc/testsuite/gcc.target/i386/harden-sls-4.c
> b/gcc/testsuite/gcc.target/i386/harden-sls-4.c
> new file mode 100644
> index 00000000000..c33147f11b5
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/harden-sls-4.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mindirect-branch=keep -mharden-sls=all" } */
> +/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
> +
> +extern void (*fptr) (void);
> +
> +void
> +foo (void)
> +{
> + fptr ();
> +}
> +
> +/* { dg-final { scan-assembler "jmp\[ \t\]+\\*_?fptr" } } */
> +/* { dg-final { scan-assembler-times "int3" 1 } } */
> --
> 2.33.1
>
