RE: [PATCH] arm64: module: Use aarch64_insn_write when updating relocations later on

From: nobuta.keiya@xxxxxxxxxxx
Date: Sun Dec 19 2021 - 23:28:22 EST

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Hi,

> > Avoid this fault by calling aarch64_insn_write() to update the instruction
> > if the module text has already been marked read-only. Preserve the current
> > behaviour if called before this has been done.
> >
> > Signed-off-by: Suraj Jitindar Singh <surajjs@xxxxxxxxxx>
> > ---
> > arch/arm64/kernel/module.c | 81 ++++++++++++++++++++++----------------
> > 1 file changed, 47 insertions(+), 34 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
> > index b5ec010c481f..35596ea870ab 100644
> > --- a/arch/arm64/kernel/module.c
> > +++ b/arch/arm64/kernel/module.c
> > @@ -19,6 +19,7 @@
> > #include <asm/alternative.h>
> > #include <asm/insn.h>
> > #include <asm/sections.h>
> > +#include <asm/patching.h>
> >
> > void *module_alloc(unsigned long size)
> > {
> > @@ -155,7 +156,8 @@ enum aarch64_insn_movw_imm_type {
> > };
> >
> > static int reloc_insn_movw(enum aarch64_reloc_op op, __le32 *place, u64 val,
> > - int lsb, enum aarch64_insn_movw_imm_type imm_type)
> > + int lsb, enum aarch64_insn_movw_imm_type imm_type,
> > + bool early)
> > {
> > u64 imm;
> > s64 sval;
> > @@ -187,7 +189,10 @@ static int reloc_insn_movw(enum aarch64_reloc_op op, __le32 *place, u64 val,
> >
> > /* Update the instruction with the new encoding. */
> > insn = aarch64_insn_encode_immediate(AARCH64_INSN_IMM_16, insn, imm);
> > - *place = cpu_to_le32(insn);
> > + if (early)
> > + *place = cpu_to_le32(insn);
> > + else
> > + aarch64_insn_write(place, insn);
>
> If we really need this, I think it'd be better to refactor the
> reloc_insn_*() helpers to generate the new encoding into a temporary
> buffer, and make it the caller's responsibiltiy to then perform the
> write to the real location in the module.
>
> That way we only have to handle the "early" distinction in one place
> rather than spreading it out.
>
> I see you haven't altered the reloc_data() function -- does livepatch
> never result in data relocations?
>
> Thanks,
> Mark.
>

Livepatch can also result in data relocation.

So I wrote data relocation test with kpatch and send pull-request [1].
Suraj, please try it if you would like.

[1] https://github.com/dynup/kpatch/pull/1244

Thanks,
Keiya

> >
> > if (imm > U16_MAX)
> > return -ERANGE;
> > @@ -196,7 +201,8 @@ static int reloc_insn_movw(enum aarch64_reloc_op op, __le32 *place, u64 val,
> > }
> >
> > static int reloc_insn_imm(enum aarch64_reloc_op op, __le32 *place, u64 val,
> > - int lsb, int len, enum aarch64_insn_imm_type imm_type)
> > + int lsb, int len, enum aarch64_insn_imm_type imm_type,
> > + bool early)
> > {
> > u64 imm, imm_mask;
> > s64 sval;
> > @@ -212,7 +218,10 @@ static int reloc_insn_imm(enum aarch64_reloc_op op, __le32 *place, u64 val,
> >
> > /* Update the instruction's immediate field. */
> > insn = aarch64_insn_encode_immediate(imm_type, insn, imm);
> > - *place = cpu_to_le32(insn);
> > + if (early)
> > + *place = cpu_to_le32(insn);
> > + else
> > + aarch64_insn_write(place, insn);
> >
> > /*
> > * Extract the upper value bits (including the sign bit) and
> > @@ -231,17 +240,17 @@ static int reloc_insn_imm(enum aarch64_reloc_op op, __le32 *place, u64 val,
> > }
> >
> > static int reloc_insn_adrp(struct module *mod, Elf64_Shdr *sechdrs,
> > - __le32 *place, u64 val)
> > + __le32 *place, u64 val, bool early)
> > {
> > u32 insn;
> >
> > if (!is_forbidden_offset_for_adrp(place))
> > return reloc_insn_imm(RELOC_OP_PAGE, place, val, 12, 21,
> > - AARCH64_INSN_IMM_ADR);
> > + AARCH64_INSN_IMM_ADR, early);
> >
> > /* patch ADRP to ADR if it is in range */
> > if (!reloc_insn_imm(RELOC_OP_PREL, place, val & ~0xfff, 0, 21,
> > - AARCH64_INSN_IMM_ADR)) {
> > + AARCH64_INSN_IMM_ADR, early)) {
> > insn = le32_to_cpu(*place);
> > insn &= ~BIT(31);
> > } else {
> > @@ -253,7 +262,10 @@ static int reloc_insn_adrp(struct module *mod, Elf64_Shdr *sechdrs,
> > AARCH64_INSN_BRANCH_NOLINK);
> > }
> >
> > - *place = cpu_to_le32(insn);
> > + if (early)
> > + *place = cpu_to_le32(insn);
> > + else
> > + aarch64_insn_write(place, insn);
> > return 0;
> > }
> >
> > @@ -270,6 +282,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> > void *loc;
> > u64 val;
> > Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
> > + bool early = me->state == MODULE_STATE_UNFORMED;
> >
> > for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
> > /* loc corresponds to P in the AArch64 ELF document. */
> > @@ -322,88 +335,88 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> > fallthrough;
> > case R_AARCH64_MOVW_UABS_G0:
> > ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 0,
> > - AARCH64_INSN_IMM_MOVKZ);
> > + AARCH64_INSN_IMM_MOVKZ, early);
> > break;
> > case R_AARCH64_MOVW_UABS_G1_NC:
> > overflow_check = false;
> > fallthrough;
> > case R_AARCH64_MOVW_UABS_G1:
> > ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 16,
> > - AARCH64_INSN_IMM_MOVKZ);
> > + AARCH64_INSN_IMM_MOVKZ, early);
> > break;
> > case R_AARCH64_MOVW_UABS_G2_NC:
> > overflow_check = false;
> > fallthrough;
> > case R_AARCH64_MOVW_UABS_G2:
> > ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 32,
> > - AARCH64_INSN_IMM_MOVKZ);
> > + AARCH64_INSN_IMM_MOVKZ, early);
> > break;
> > case R_AARCH64_MOVW_UABS_G3:
> > /* We're using the top bits so we can't overflow. */
> > overflow_check = false;
> > ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 48,
> > - AARCH64_INSN_IMM_MOVKZ);
> > + AARCH64_INSN_IMM_MOVKZ, early);
> > break;
> > case R_AARCH64_MOVW_SABS_G0:
> > ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 0,
> > - AARCH64_INSN_IMM_MOVNZ);
> > + AARCH64_INSN_IMM_MOVNZ, early);
> > break;
> > case R_AARCH64_MOVW_SABS_G1:
> > ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 16,
> > - AARCH64_INSN_IMM_MOVNZ);
> > + AARCH64_INSN_IMM_MOVNZ, early);
> > break;
> > case R_AARCH64_MOVW_SABS_G2:
> > ovf = reloc_insn_movw(RELOC_OP_ABS, loc, val, 32,
> > - AARCH64_INSN_IMM_MOVNZ);
> > + AARCH64_INSN_IMM_MOVNZ, early);
> > break;
> > case R_AARCH64_MOVW_PREL_G0_NC:
> > overflow_check = false;
> > ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 0,
> > - AARCH64_INSN_IMM_MOVKZ);
> > + AARCH64_INSN_IMM_MOVKZ, early);
> > break;
> > case R_AARCH64_MOVW_PREL_G0:
> > ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 0,
> > - AARCH64_INSN_IMM_MOVNZ);
> > + AARCH64_INSN_IMM_MOVNZ, early);
> > break;
> > case R_AARCH64_MOVW_PREL_G1_NC:
> > overflow_check = false;
> > ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 16,
> > - AARCH64_INSN_IMM_MOVKZ);
> > + AARCH64_INSN_IMM_MOVKZ, early);
> > break;
> > case R_AARCH64_MOVW_PREL_G1:
> > ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 16,
> > - AARCH64_INSN_IMM_MOVNZ);
> > + AARCH64_INSN_IMM_MOVNZ, early);
> > break;
> > case R_AARCH64_MOVW_PREL_G2_NC:
> > overflow_check = false;
> > ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 32,
> > - AARCH64_INSN_IMM_MOVKZ);
> > + AARCH64_INSN_IMM_MOVKZ, early);
> > break;
> > case R_AARCH64_MOVW_PREL_G2:
> > ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 32,
> > - AARCH64_INSN_IMM_MOVNZ);
> > + AARCH64_INSN_IMM_MOVNZ, early);
> > break;
> > case R_AARCH64_MOVW_PREL_G3:
> > /* We're using the top bits so we can't overflow. */
> > overflow_check = false;
> > ovf = reloc_insn_movw(RELOC_OP_PREL, loc, val, 48,
> > - AARCH64_INSN_IMM_MOVNZ);
> > + AARCH64_INSN_IMM_MOVNZ, early);
> > break;
> >
> > /* Immediate instruction relocations. */
> > case R_AARCH64_LD_PREL_LO19:
> > ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 19,
> > - AARCH64_INSN_IMM_19);
> > + AARCH64_INSN_IMM_19, early);
> > break;
> > case R_AARCH64_ADR_PREL_LO21:
> > ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 0, 21,
> > - AARCH64_INSN_IMM_ADR);
> > + AARCH64_INSN_IMM_ADR, early);
> > break;
> > case R_AARCH64_ADR_PREL_PG_HI21_NC:
> > overflow_check = false;
> > fallthrough;
> > case R_AARCH64_ADR_PREL_PG_HI21:
> > - ovf = reloc_insn_adrp(me, sechdrs, loc, val);
> > + ovf = reloc_insn_adrp(me, sechdrs, loc, val, early);
> > if (ovf && ovf != -ERANGE)
> > return ovf;
> > break;
> > @@ -411,40 +424,40 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> > case R_AARCH64_LDST8_ABS_LO12_NC:
> > overflow_check = false;
> > ovf = reloc_insn_imm(RELOC_OP_ABS, loc, val, 0, 12,
> > - AARCH64_INSN_IMM_12);
> > + AARCH64_INSN_IMM_12, early);
> > break;
> > case R_AARCH64_LDST16_ABS_LO12_NC:
> > overflow_check = false;
> > ovf = reloc_insn_imm(RELOC_OP_ABS, loc, val, 1, 11,
> > - AARCH64_INSN_IMM_12);
> > + AARCH64_INSN_IMM_12, early);
> > break;
> > case R_AARCH64_LDST32_ABS_LO12_NC:
> > overflow_check = false;
> > ovf = reloc_insn_imm(RELOC_OP_ABS, loc, val, 2, 10,
> > - AARCH64_INSN_IMM_12);
> > + AARCH64_INSN_IMM_12, early);
> > break;
> > case R_AARCH64_LDST64_ABS_LO12_NC:
> > overflow_check = false;
> > ovf = reloc_insn_imm(RELOC_OP_ABS, loc, val, 3, 9,
> > - AARCH64_INSN_IMM_12);
> > + AARCH64_INSN_IMM_12, early);
> > break;
> > case R_AARCH64_LDST128_ABS_LO12_NC:
> > overflow_check = false;
> > ovf = reloc_insn_imm(RELOC_OP_ABS, loc, val, 4, 8,
> > - AARCH64_INSN_IMM_12);
> > + AARCH64_INSN_IMM_12, early);
> > break;
> > case R_AARCH64_TSTBR14:
> > ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 14,
> > - AARCH64_INSN_IMM_14);
> > + AARCH64_INSN_IMM_14, early);
> > break;
> > case R_AARCH64_CONDBR19:
> > ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 19,
> > - AARCH64_INSN_IMM_19);
> > + AARCH64_INSN_IMM_19, early);
> > break;
> > case R_AARCH64_JUMP26:
> > case R_AARCH64_CALL26:
> > ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 26,
> > - AARCH64_INSN_IMM_26);
> > + AARCH64_INSN_IMM_26, early);
> >
> > if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
> > ovf == -ERANGE) {
> > @@ -452,7 +465,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> > if (!val)
> > return -ENOEXEC;
> > ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2,
> > - 26, AARCH64_INSN_IMM_26);
> > + 26, AARCH64_INSN_IMM_26, early);
> > }
> > break;
> >
> > --
> > 2.17.1
> >

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