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powerpc/44x: Implement Kernel Userspace Exec Protection (KUEP)

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Powerpc 44x has two bits for exec protection in TLBs: one
for user (UX) and one for superviser (SX).

Clear SX on user pages in TLB miss handlers to provide KUEP.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/169310e08152aa1d96c979770291d165ec6896ae.1622616032.git.christophe.leroy@csgroup.eu
This commit is contained in:
Christophe Leroy 2021-06-02 06:42:10 +00:00 committed by Michael Ellerman
parent c0ca0fe08c
commit 10248dcba1
4 changed files with 23 additions and 0 deletions
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1
arch/powerpc/include/asm/nohash/32/mmu-44x.h
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@ -113,6 +113,7 @@ typedef struct {
/* patch sites */ /* patch sites */
extern s32 patch__tlb_44x_hwater_D, patch__tlb_44x_hwater_I; extern s32 patch__tlb_44x_hwater_D, patch__tlb_44x_hwater_I;
extern s32 patch__tlb_44x_kuep, patch__tlb_47x_kuep;
#endif /* !__ASSEMBLY__ */ #endif /* !__ASSEMBLY__ */

8
arch/powerpc/kernel/head_44x.S
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@ -532,6 +532,10 @@ finish_tlb_load_44x:
andi. r10,r12,_PAGE_USER /* User page ? */ andi. r10,r12,_PAGE_USER /* User page ? */
beq 1f /* nope, leave U bits empty */ beq 1f /* nope, leave U bits empty */
rlwimi r11,r11,3,26,28 /* yes, copy S bits to U */ rlwimi r11,r11,3,26,28 /* yes, copy S bits to U */
#ifdef CONFIG_PPC_KUEP
0: rlwinm r11,r11,0,~PPC44x_TLB_SX /* Clear SX if User page */
patch_site 0b, patch__tlb_44x_kuep
#endif
1: tlbwe r11,r13,PPC44x_TLB_ATTRIB /* Write ATTRIB */ 1: tlbwe r11,r13,PPC44x_TLB_ATTRIB /* Write ATTRIB */
/* Done...restore registers and get out of here. /* Done...restore registers and get out of here.
@ -743,6 +747,10 @@ finish_tlb_load_47x:
andi. r10,r12,_PAGE_USER /* User page ? */ andi. r10,r12,_PAGE_USER /* User page ? */
beq 1f /* nope, leave U bits empty */ beq 1f /* nope, leave U bits empty */
rlwimi r11,r11,3,26,28 /* yes, copy S bits to U */ rlwimi r11,r11,3,26,28 /* yes, copy S bits to U */
#ifdef CONFIG_PPC_KUEP
0: rlwinm r11,r11,0,~PPC47x_TLB2_SX /* Clear SX if User page */
patch_site 0b, patch__tlb_47x_kuep
#endif
1: tlbwe r11,r13,2 1: tlbwe r11,r13,2
/* Done...restore registers and get out of here. /* Done...restore registers and get out of here.

13
arch/powerpc/mm/nohash/44x.c
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@ -239,3 +239,16 @@ void __init mmu_init_secondary(int cpu)
} }
} }
#endif /* CONFIG_SMP */ #endif /* CONFIG_SMP */
#ifdef CONFIG_PPC_KUEP
void __init setup_kuep(bool disabled)
{
if (disabled)
patch_instruction_site(&patch__tlb_44x_kuep, ppc_inst(PPC_RAW_NOP()));
else
pr_info("Activating Kernel Userspace Execution Prevention\n");
if (IS_ENABLED(CONFIG_PPC_47x) && disabled)
patch_instruction_site(&patch__tlb_47x_kuep, ppc_inst(PPC_RAW_NOP()));
}
#endif

1
arch/powerpc/platforms/Kconfig.cputype
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@ -61,6 +61,7 @@ config 44x
select 4xx_SOC select 4xx_SOC
select HAVE_PCI select HAVE_PCI
select PHYS_64BIT select PHYS_64BIT
select PPC_HAVE_KUEP
endchoice endchoice