[v5] x86-64: Stack protector and percpu improvements

[PATCH v5 06/16] x86/relocs: Handle R_X86_64_REX_GOTPCRELX relocations

Posted by Brian Gerst 2 weeks, 4 days ago

Clang may produce R_X86_64_REX_GOTPCRELX relocations when redefining the
stack protector location.  Treat them as another type of PC-relative
relocation.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
---
 arch/x86/tools/relocs.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index 6afe2e5e9102..7d7fc7f0a250 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -32,6 +32,11 @@ static struct relocs		relocs32;
 static struct relocs		relocs32neg;
 static struct relocs		relocs64;
 # define FMT PRIu64
+
+#ifndef R_X86_64_REX_GOTPCRELX
+#define R_X86_64_REX_GOTPCRELX 42
+#endif
+
 #else
 # define FMT PRIu32
 #endif
@@ -226,6 +231,7 @@ static const char *rel_type(unsigned type)
 		REL_TYPE(R_X86_64_PC16),
 		REL_TYPE(R_X86_64_8),
 		REL_TYPE(R_X86_64_PC8),
+		REL_TYPE(R_X86_64_REX_GOTPCRELX),
 #else
 		REL_TYPE(R_386_NONE),
 		REL_TYPE(R_386_32),
@@ -860,6 +866,7 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
 
 	case R_X86_64_PC32:
 	case R_X86_64_PLT32:
+	case R_X86_64_REX_GOTPCRELX:
 		/*
 		 * PC relative relocations don't need to be adjusted unless
 		 * referencing a percpu symbol.
-- 
2.47.0

Re: [PATCH v5 06/16] x86/relocs: Handle R_X86_64_REX_GOTPCRELX relocations

Posted by Uros Bizjak 2 weeks, 3 days ago

On Tue, Nov 5, 2024 at 4:58 PM Brian Gerst <brgerst@gmail.com> wrote:
>
> Clang may produce R_X86_64_REX_GOTPCRELX relocations when redefining the
> stack protector location.  Treat them as another type of PC-relative
> relocation.
>
> Signed-off-by: Brian Gerst <brgerst@gmail.com>
> ---
>  arch/x86/tools/relocs.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
> index 6afe2e5e9102..7d7fc7f0a250 100644
> --- a/arch/x86/tools/relocs.c
> +++ b/arch/x86/tools/relocs.c
> @@ -32,6 +32,11 @@ static struct relocs         relocs32;
>  static struct relocs           relocs32neg;
>  static struct relocs           relocs64;
>  # define FMT PRIu64
> +
> +#ifndef R_X86_64_REX_GOTPCRELX
> +#define R_X86_64_REX_GOTPCRELX 42
> +#endif

The next patch (7/16) introduces the above definition to
arch/x86/include/asm/elf.h. If you swap patches 6 and 7 in the series,
you won't have to introduce the above conditional definition.

Uros.

> +
>  #else
>  # define FMT PRIu32
>  #endif
> @@ -226,6 +231,7 @@ static const char *rel_type(unsigned type)
>                 REL_TYPE(R_X86_64_PC16),
>                 REL_TYPE(R_X86_64_8),
>                 REL_TYPE(R_X86_64_PC8),
> +               REL_TYPE(R_X86_64_REX_GOTPCRELX),
>  #else
>                 REL_TYPE(R_386_NONE),
>                 REL_TYPE(R_386_32),
> @@ -860,6 +866,7 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
>
>         case R_X86_64_PC32:
>         case R_X86_64_PLT32:
> +       case R_X86_64_REX_GOTPCRELX:
>                 /*
>                  * PC relative relocations don't need to be adjusted unless
>                  * referencing a percpu symbol.
> --
> 2.47.0
>

Re: [PATCH v5 06/16] x86/relocs: Handle R_X86_64_REX_GOTPCRELX relocations

Posted by Brian Gerst 2 weeks, 3 days ago

On Thu, Nov 7, 2024 at 6:20 AM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> On Tue, Nov 5, 2024 at 4:58 PM Brian Gerst <brgerst@gmail.com> wrote:
> >
> > Clang may produce R_X86_64_REX_GOTPCRELX relocations when redefining the
> > stack protector location.  Treat them as another type of PC-relative
> > relocation.
> >
> > Signed-off-by: Brian Gerst <brgerst@gmail.com>
> > ---
> >  arch/x86/tools/relocs.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
> > index 6afe2e5e9102..7d7fc7f0a250 100644
> > --- a/arch/x86/tools/relocs.c
> > +++ b/arch/x86/tools/relocs.c
> > @@ -32,6 +32,11 @@ static struct relocs         relocs32;
> >  static struct relocs           relocs32neg;
> >  static struct relocs           relocs64;
> >  # define FMT PRIu64
> > +
> > +#ifndef R_X86_64_REX_GOTPCRELX
> > +#define R_X86_64_REX_GOTPCRELX 42
> > +#endif
>
> The next patch (7/16) introduces the above definition to
> arch/x86/include/asm/elf.h. If you swap patches 6 and 7 in the series,
> you won't have to introduce the above conditional definition.
>
> Uros.

This is a userspace tool, so it's using the build host libc headers.

--
Brian Gerst

Re: [PATCH v5 06/16] x86/relocs: Handle R_X86_64_REX_GOTPCRELX relocations

Posted by Uros Bizjak 2 weeks, 3 days ago

On Thu, Nov 7, 2024 at 12:27 PM Brian Gerst <brgerst@gmail.com> wrote:
>
> On Thu, Nov 7, 2024 at 6:20 AM Uros Bizjak <ubizjak@gmail.com> wrote:
> >
> > On Tue, Nov 5, 2024 at 4:58 PM Brian Gerst <brgerst@gmail.com> wrote:
> > >
> > > Clang may produce R_X86_64_REX_GOTPCRELX relocations when redefining the
> > > stack protector location.  Treat them as another type of PC-relative
> > > relocation.
> > >
> > > Signed-off-by: Brian Gerst <brgerst@gmail.com>
> > > ---
> > >  arch/x86/tools/relocs.c | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > >
> > > diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
> > > index 6afe2e5e9102..7d7fc7f0a250 100644
> > > --- a/arch/x86/tools/relocs.c
> > > +++ b/arch/x86/tools/relocs.c
> > > @@ -32,6 +32,11 @@ static struct relocs         relocs32;
> > >  static struct relocs           relocs32neg;
> > >  static struct relocs           relocs64;
> > >  # define FMT PRIu64
> > > +
> > > +#ifndef R_X86_64_REX_GOTPCRELX
> > > +#define R_X86_64_REX_GOTPCRELX 42
> > > +#endif
> >
> > The next patch (7/16) introduces the above definition to
> > arch/x86/include/asm/elf.h. If you swap patches 6 and 7 in the series,
> > you won't have to introduce the above conditional definition.
>
> This is a userspace tool, so it's using the build host libc headers.

Ah, indeed.

Thanks,
Uros.