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Message-ID: <CAJM55Z9zb_pOQyJcj=GcamyU3V-iqxMmOkOGRpD7a6mqszLpuQ@mail.gmail.com>
Date: Wed, 18 Oct 2023 13:28:58 -0700
From: Emil Renner Berthing <emil.renner.berthing@...onical.com>
To: Charlie Jenkins <charlie@...osinc.com>,
Emil Renner Berthing <emil.renner.berthing@...onical.com>
Cc: linux-riscv@...ts.infradead.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Eric Biederman <ebiederm@...ssion.com>,
Kees Cook <keescook@...omium.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>
Subject: Re: [PATCH v4 1/2] riscv: Add remaining module relocations
Charlie Jenkins wrote:
> On Wed, Oct 18, 2023 at 11:38:39AM -0700, Emil Renner Berthing wrote:
> > Charlie Jenkins wrote:
> > > On Wed, Oct 18, 2023 at 05:17:44AM -0700, Emil Renner Berthing wrote:
> > > > Charlie Jenkins wrote:
> > > > > Add all final module relocations and add error logs explaining the ones
> > > > > that are not supported.
> > > > >
> > > > > Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> > > > > ---
> > > > > arch/riscv/include/uapi/asm/elf.h | 5 +-
> > > > > arch/riscv/kernel/module.c | 207 +++++++++++++++++++++++++++++++++-----
> > > > > 2 files changed, 186 insertions(+), 26 deletions(-)
> > > > >
> > > > > diff --git a/arch/riscv/include/uapi/asm/elf.h b/arch/riscv/include/uapi/asm/elf.h
> > > > > index d696d6610231..11a71b8533d5 100644
> > > > > --- a/arch/riscv/include/uapi/asm/elf.h
> > > > > +++ b/arch/riscv/include/uapi/asm/elf.h
> > > > > @@ -49,6 +49,7 @@ typedef union __riscv_fp_state elf_fpregset_t;
> > > > > #define R_RISCV_TLS_DTPREL64 9
> > > > > #define R_RISCV_TLS_TPREL32 10
> > > > > #define R_RISCV_TLS_TPREL64 11
> > > > > +#define R_RISCV_IRELATIVE 58
> > > > >
> > > > > /* Relocation types not used by the dynamic linker */
> > > > > #define R_RISCV_BRANCH 16
> > > > > @@ -81,7 +82,6 @@ typedef union __riscv_fp_state elf_fpregset_t;
> > > > > #define R_RISCV_ALIGN 43
> > > > > #define R_RISCV_RVC_BRANCH 44
> > > > > #define R_RISCV_RVC_JUMP 45
> > > > > -#define R_RISCV_LUI 46
> > > > > #define R_RISCV_GPREL_I 47
> > > > > #define R_RISCV_GPREL_S 48
> > > > > #define R_RISCV_TPREL_I 49
> > > > > @@ -93,6 +93,9 @@ typedef union __riscv_fp_state elf_fpregset_t;
> > > > > #define R_RISCV_SET16 55
> > > > > #define R_RISCV_SET32 56
> > > > > #define R_RISCV_32_PCREL 57
> > > > > +#define R_RISCV_PLT32 59
> > > > > +#define R_RISCV_SET_ULEB128 60
> > > > > +#define R_RISCV_SUB_ULEB128 61
> > > > >
> > > > >
> > > > > #endif /* _UAPI_ASM_RISCV_ELF_H */
> > > > > diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
> > > > > index 7c651d55fcbd..e860726352ac 100644
> > > > > --- a/arch/riscv/kernel/module.c
> > > > > +++ b/arch/riscv/kernel/module.c
> > > > > @@ -7,6 +7,7 @@
> > > > > #include <linux/elf.h>
> > > > > #include <linux/err.h>
> > > > > #include <linux/errno.h>
> > > > > +#include <linux/kernel.h>
> > > > > #include <linux/moduleloader.h>
> > > > > #include <linux/vmalloc.h>
> > > > > #include <linux/sizes.h>
> > > > > @@ -268,6 +269,12 @@ static int apply_r_riscv_align_rela(struct module *me, u32 *location,
> > > > > return -EINVAL;
> > > > > }
> > > > >
> > > > > +static int apply_r_riscv_add8_rela(struct module *me, u32 *location, Elf_Addr v)
> > > > > +{
> > > > > + *(u8 *)location += (u8)v;
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > static int apply_r_riscv_add16_rela(struct module *me, u32 *location,
> > > > > Elf_Addr v)
> > > > > {
> > > > > @@ -289,6 +296,12 @@ static int apply_r_riscv_add64_rela(struct module *me, u32 *location,
> > > > > return 0;
> > > > > }
> > > > >
> > > > > +static int apply_r_riscv_sub8_rela(struct module *me, u32 *location, Elf_Addr v)
> > > > > +{
> > > > > + *(u8 *)location -= (u8)v;
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > static int apply_r_riscv_sub16_rela(struct module *me, u32 *location,
> > > > > Elf_Addr v)
> > > > > {
> > > > > @@ -310,31 +323,149 @@ static int apply_r_riscv_sub64_rela(struct module *me, u32 *location,
> > > > > return 0;
> > > > > }
> > > > >
> > > > > -static int (*reloc_handlers_rela[]) (struct module *me, u32 *location,
> > > > > - Elf_Addr v) = {
> > > > > - [R_RISCV_32] = apply_r_riscv_32_rela,
> > > > > - [R_RISCV_64] = apply_r_riscv_64_rela,
> > > > > - [R_RISCV_BRANCH] = apply_r_riscv_branch_rela,
> > > > > - [R_RISCV_JAL] = apply_r_riscv_jal_rela,
> > > > > - [R_RISCV_RVC_BRANCH] = apply_r_riscv_rvc_branch_rela,
> > > > > - [R_RISCV_RVC_JUMP] = apply_r_riscv_rvc_jump_rela,
> > > > > - [R_RISCV_PCREL_HI20] = apply_r_riscv_pcrel_hi20_rela,
> > > > > - [R_RISCV_PCREL_LO12_I] = apply_r_riscv_pcrel_lo12_i_rela,
> > > > > - [R_RISCV_PCREL_LO12_S] = apply_r_riscv_pcrel_lo12_s_rela,
> > > > > - [R_RISCV_HI20] = apply_r_riscv_hi20_rela,
> > > > > - [R_RISCV_LO12_I] = apply_r_riscv_lo12_i_rela,
> > > > > - [R_RISCV_LO12_S] = apply_r_riscv_lo12_s_rela,
> > > > > - [R_RISCV_GOT_HI20] = apply_r_riscv_got_hi20_rela,
> > > > > - [R_RISCV_CALL_PLT] = apply_r_riscv_call_plt_rela,
> > > > > - [R_RISCV_CALL] = apply_r_riscv_call_rela,
> > > > > - [R_RISCV_RELAX] = apply_r_riscv_relax_rela,
> > > > > - [R_RISCV_ALIGN] = apply_r_riscv_align_rela,
> > > > > - [R_RISCV_ADD16] = apply_r_riscv_add16_rela,
> > > > > - [R_RISCV_ADD32] = apply_r_riscv_add32_rela,
> > > > > - [R_RISCV_ADD64] = apply_r_riscv_add64_rela,
> > > > > - [R_RISCV_SUB16] = apply_r_riscv_sub16_rela,
> > > > > - [R_RISCV_SUB32] = apply_r_riscv_sub32_rela,
> > > > > - [R_RISCV_SUB64] = apply_r_riscv_sub64_rela,
> > > > > +static int dynamic_linking_not_supported(struct module *me, u32 *location,
> > > > > + Elf_Addr v)
> > > > > +{
> > > > > + pr_err("%s: Dynamic linking not supported in kernel modules PC = %p\n",
> > > > > + me->name, location);
> > > > > + return -EINVAL;
> > > > > +}
> > > > > +
> > > > > +static int tls_not_supported(struct module *me, u32 *location, Elf_Addr v)
> > > > > +{
> > > > > + pr_err("%s: Thread local storage not supported in kernel modules PC = %p\n",
> > > > > + me->name, location);
> > > > > + return -EINVAL;
> > > > > +}
> > > > > +
> > > > > +static int apply_r_riscv_sub6_rela(struct module *me, u32 *location, Elf_Addr v)
> > > > > +{
> > > > > + *(u8 *)location = (*location - ((u8)v & 0x3F)) & 0x3F;
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +static int apply_r_riscv_set6_rela(struct module *me, u32 *location, Elf_Addr v)
> > > > > +{
> > > > > + *(u8 *)location = (*(u8 *)location & 0xc0) | ((u8)v & 0x3F);
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +static int apply_r_riscv_set8_rela(struct module *me, u32 *location, Elf_Addr v)
> > > > > +{
> > > > > + *(u8 *)location = (u8)v;
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +static int apply_r_riscv_set16_rela(struct module *me, u32 *location,
> > > > > + Elf_Addr v)
> > > > > +{
> > > > > + *(u16 *)location = (u16)v;
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +static int apply_r_riscv_set32_rela(struct module *me, u32 *location,
> > > > > + Elf_Addr v)
> > > > > +{
> > > > > + *(u32 *)location = (u32)v;
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +static int apply_r_riscv_32_pcrel_rela(struct module *me, u32 *location,
> > > > > + Elf_Addr v)
> > > > > +{
> > > > > + *(u32 *)location = (u32)v;
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +static int apply_r_riscv_plt32_rela(struct module *me, u32 *location,
> > > > > + Elf_Addr v)
> > > > > +{
> > > > > + *(u32 *)location = (u32)v;
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +static int apply_r_riscv_set_uleb128(struct module *me, u32 *location, Elf_Addr v)
> > > > > +{
> > > > > + /*
> > > > > + * Relocation is only performed if R_RISCV_SET_ULEB128 is followed by
> > > > > + * R_RISCV_SUB_ULEB128 so do computation there
> > > > > + */
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +static int apply_r_riscv_sub_uleb128(struct module *me, u32 *location, Elf_Addr v)
> > > > > +{
> > > > > + if (v >= 128) {
> > > > > + pr_err("%s: uleb128 must be in [0, 127] (not %ld) at PC = %p\n",
> > > > > + me->name, (unsigned long)v, location);
> > > > > + return -EINVAL;
> > > > > + }
> > > > > +
> > > > > + *location = v;
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +/*
> > > > > + * Relocations defined in the riscv-elf-psabi-doc.
> > > > > + * This handles static linking only.
> > > > > + */
> > > > > +static int (*reloc_handlers_rela[])(struct module *me, u32 *location,
> > > > > + Elf_Addr v) = {
> > > > > + [R_RISCV_32] = apply_r_riscv_32_rela,
> > > > > + [R_RISCV_64] = apply_r_riscv_64_rela,
> > > > > + [R_RISCV_RELATIVE] = dynamic_linking_not_supported,
> > > > > + [R_RISCV_COPY] = dynamic_linking_not_supported,
> > > > > + [R_RISCV_JUMP_SLOT] = dynamic_linking_not_supported,
> > > > > + [R_RISCV_TLS_DTPMOD32] = dynamic_linking_not_supported,
> > > > > + [R_RISCV_TLS_DTPMOD64] = dynamic_linking_not_supported,
> > > > > + [R_RISCV_TLS_DTPREL32] = dynamic_linking_not_supported,
> > > > > + [R_RISCV_TLS_DTPREL64] = dynamic_linking_not_supported,
> > > > > + [R_RISCV_TLS_TPREL32] = dynamic_linking_not_supported,
> > > > > + [R_RISCV_TLS_TPREL64] = dynamic_linking_not_supported,
> > > > > + /* 12-15 undefined */
> > > > > + [R_RISCV_BRANCH] = apply_r_riscv_branch_rela,
> > > > > + [R_RISCV_JAL] = apply_r_riscv_jal_rela,
> > > > > + [R_RISCV_CALL] = apply_r_riscv_call_rela,
> > > > > + [R_RISCV_CALL_PLT] = apply_r_riscv_call_plt_rela,
> > > > > + [R_RISCV_GOT_HI20] = apply_r_riscv_got_hi20_rela,
> > > > > + [R_RISCV_TLS_GOT_HI20] = tls_not_supported,
> > > > > + [R_RISCV_TLS_GD_HI20] = tls_not_supported,
> > > > > + [R_RISCV_PCREL_HI20] = apply_r_riscv_pcrel_hi20_rela,
> > > > > + [R_RISCV_PCREL_LO12_I] = apply_r_riscv_pcrel_lo12_i_rela,
> > > > > + [R_RISCV_PCREL_LO12_S] = apply_r_riscv_pcrel_lo12_s_rela,
> > > > > + [R_RISCV_HI20] = apply_r_riscv_hi20_rela,
> > > > > + [R_RISCV_LO12_I] = apply_r_riscv_lo12_i_rela,
> > > > > + [R_RISCV_LO12_S] = apply_r_riscv_lo12_s_rela,
> > > > > + [R_RISCV_TPREL_HI20] = tls_not_supported,
> > > > > + [R_RISCV_TPREL_LO12_I] = tls_not_supported,
> > > > > + [R_RISCV_TPREL_LO12_S] = tls_not_supported,
> > > > > + [R_RISCV_TPREL_ADD] = tls_not_supported,
> > > > > + [R_RISCV_ADD8] = apply_r_riscv_add8_rela,
> > > > > + [R_RISCV_ADD16] = apply_r_riscv_add16_rela,
> > > > > + [R_RISCV_ADD32] = apply_r_riscv_add32_rela,
> > > > > + [R_RISCV_ADD64] = apply_r_riscv_add64_rela,
> > > > > + [R_RISCV_SUB8] = apply_r_riscv_sub8_rela,
> > > > > + [R_RISCV_SUB16] = apply_r_riscv_sub16_rela,
> > > > > + [R_RISCV_SUB32] = apply_r_riscv_sub32_rela,
> > > > > + [R_RISCV_SUB64] = apply_r_riscv_sub64_rela,
> > > > > + /* 41-42 reserved for future standard use */
> > > > > + [R_RISCV_ALIGN] = apply_r_riscv_align_rela,
> > > > > + [R_RISCV_RVC_BRANCH] = apply_r_riscv_rvc_branch_rela,
> > > > > + [R_RISCV_RVC_JUMP] = apply_r_riscv_rvc_jump_rela,
> > > > > + /* 46-50 reserved for future standard use */
> > > > > + [R_RISCV_RELAX] = apply_r_riscv_relax_rela,
> > > > > + [R_RISCV_SUB6] = apply_r_riscv_sub6_rela,
> > > > > + [R_RISCV_SET6] = apply_r_riscv_set6_rela,
> > > > > + [R_RISCV_SET8] = apply_r_riscv_set8_rela,
> > > > > + [R_RISCV_SET16] = apply_r_riscv_set16_rela,
> > > > > + [R_RISCV_SET32] = apply_r_riscv_set32_rela,
> > > > > + [R_RISCV_32_PCREL] = apply_r_riscv_32_pcrel_rela,
> > > > > + [R_RISCV_IRELATIVE] = dynamic_linking_not_supported,
> > > > > + [R_RISCV_PLT32] = apply_r_riscv_plt32_rela,
> > > > > + [R_RISCV_SET_ULEB128] = apply_r_riscv_set_uleb128,
> > > > > + [R_RISCV_SUB_ULEB128] = apply_r_riscv_sub_uleb128,
> > > > > + /* 62-191 reserved for future standard use */
> > > > > + /* 192-255 nonstandard ABI extensions */
> > > > > };
> > > >
> > > > Hi Charlie,
> > > >
> > > > This is not a critique of this patch, but all these callbacks take a
> > > > u32 *location and
> > > > because of the compressed instructions this pointer may not be
> > > > aligned, so a lot of
> > > > the callbacks end up doing unaligned access which may fault to an
> > > > M-mode handler on
> > > > some platforms.
> > > >
> > > > I once sent a patch to fix this:
> > > > https://lore.kernel.org/linux-riscv/20220224152456.493365-2-kernel@esmil.dk/
> > > >
> > > > Maybe that's something you want to look into while touching this code anyway.
> > > >
> > > > /Emil
> > >
> > > Oh nice, I will pick up that patch and change the "native-endian"
> > > wording to be "little-endian" in the commit.
> >
> > Great, thanks. You'll probably also want the reads to be wrapped in
> > le16_to_cpu() and similar when writing now that it's decided that the parcels
> > are always in little-endian byteorder.
> >
> > /Emil
>
> I believe that le16_to_cpu() is only needed when instructions are being modified, and
> the relocations that only touch data can be left alone. Is this correct?
Yes, that sounds right to me. I only meant in the riscv_insn_rmw() function of
my patch and the callbacks modifying a compressed instruction, but I haven't
gone through all the other reloc types to check if they have a set endianess.
/Emil
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