From: Nicholas Piggin npiggin@gmail.com
[ Upstream commit cb2b53cbffe3c388cd676b63f34e54ceb2643ae2 ]
Writing the AMR register is documented to require context synchronizing operations before and after, for it to take effect as expected. The KUAP restore at interrupt exit time deliberately avoids the isync after the AMR update because it only needs to take effect after the context synchronizing RFID that soon follows. Add a comment for this.
The missing isync before the update doesn't have an obvious justification, and seems it could theoretically allow a rogue user access to leak past the AMR update. Add isyncs for these.
Signed-off-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20200429065654.1677541-3-npiggin@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/include/asm/book3s/64/kup-radix.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/book3s/64/kup-radix.h b/arch/powerpc/include/asm/book3s/64/kup-radix.h index 3bcef989a35d..101d60f16d46 100644 --- a/arch/powerpc/include/asm/book3s/64/kup-radix.h +++ b/arch/powerpc/include/asm/book3s/64/kup-radix.h @@ -16,7 +16,9 @@ #ifdef CONFIG_PPC_KUAP BEGIN_MMU_FTR_SECTION_NESTED(67) ld \gpr, STACK_REGS_KUAP(r1) + isync mtspr SPRN_AMR, \gpr + /* No isync required, see kuap_restore_amr() */ END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_RADIX_KUAP, 67) #endif .endm @@ -62,8 +64,15 @@
static inline void kuap_restore_amr(struct pt_regs *regs) { - if (mmu_has_feature(MMU_FTR_RADIX_KUAP)) + if (mmu_has_feature(MMU_FTR_RADIX_KUAP)) { + isync(); mtspr(SPRN_AMR, regs->kuap); + /* + * No isync required here because we are about to RFI back to + * previous context before any user accesses would be made, + * which is a CSI. + */ + } }
static inline void kuap_check_amr(void)